So the picture from the In Amenas gas field in Algeria is still a confused one. It looks like some hostages are still being held by Islamists, although precise numbers are unclear. It also seems that a number of casualties are likely in the crisis.
We are now closing this Live Report but before we do, here is a run-through of the main developments so far:
- APS news agency reported that Algerian special forces freed more than 670 hostages including 573 Algerians and about 100 foreigners. It also quotes a source saying a total of 12 hostages have been killed in the operation, while seven foreigners are still reportedly being held;
- Some of those who made it out told Friday of how people had explosives wrapped around their necks or hid under beds as the hostage-takers struck. APS quoted a government official saying the militants were armed with missiles, rocket launchers, explosives belts and small arms;
- The US said it would not negotiate with "terrorists" after the leader of the hostage-takers reportedly proposed a prisoner swap deal;
- Algeria has faced criticism over the operation from countries including Japan, which said it was "deeply worried" that the north African nation carried it out and called for the protection of human life to be a priority.
Make sure you follow all the breaking developments in this fast-moving story as they happen with AFP's regular coverage.
1846 GMT: More on that hostage death toll -- APS is quoting a security official saying it is a provisional figure since the start of the operation.
"As well as the 18 terrorists who were killed, 12 Algerian and foreign workers died," said the source, without giving details of the nationality or number of foreign casualties.
1832 GMT: Norway's PM Jens Stoltenberg has just said his country should be prepared for "bad news" over the weekend on the fate of eight Norwegian hostages still missing.
He joins the leaders of other nations including Britain who have issued similar warnings.
1823 GMT: HOSTAGE-TAKERS STILL HOLDING SEVEN FOREIGNERS: ANI
1817 GMT: 12 HOSTAGES KILLED IN ALGERIA RESCUE BID: APS
1815 GMT: An AFP photographer on the ground near the scene just reported seeing trucks delivering empty coffins to the hospital at In Amenas, where the wounded were taken.
1802 GMT: US Defense Secretary Leon Panetta and British PM David Cameron met this afternoon at Downing Street in London and discussed the crisis.
Cameron's office has just put out a statement saying they "agreed that the incident reinforced the need to work together and with governments in the region to defeat terrorism and especially AQIM operating in the Sahel.
"They agreed on the importance of strong support for international efforts, led by the French, to assist the Malian government and deny terrorists a safe haven in Mali."
1754 GMT: Neuroscientist Siddiqui is a Pakistani woman educated at the prestigious Massachusetts Institute of Technology who was convicted in 2010 of trying to kill US servicemen in Afghanistan.
1748 GMT: Following the US reaction, let's revisit the details of that proposed prisoner swap which ANI reported on earlier.
The news agency quoted sources close to Mokhtar Belmokhtar, leader of the group which has claimed responsibility for the attack, saying they wanted to exchange American hostages for prisoners held in the US.
He reportedly proposed a swap involving Egyptian Omar Abdul Rahman and Pakistani Aafiah Siddiqui, jailed on terrorism charges.
Abdul Rahman was convicted in 1995 for his role in a 1993 attack on the World Trade Centre in New York, in which six people died.
1741 GMT: More on that breaking news -- "the United States does not negotiate with terrorists," State Department spokeswoman Victoria Nuland told reporters.
She was speaking after the Islamist gunmen who seized the gas field hostages proposed a prisoner swap.
1735 GMT: US SAYS WON'T NEGOTIATE HOSTAGE SWAP WITH 'TERRORISTS'
1728 GMT: After the Islamist group behind the Algeria siege called for an end to French intervention in Mali, France remains defiant about its position, with 1,800 French troops now on the ground in Mali.
"France on Friday framed the deadly hostage crisis in Algeria as a wake-up call to the world as it pushed for greater support for a military campaign against Islamists in neighbouring Mali," AFP's Angus MacKinnon writes.
"With Americans, Britons, Japanese and nationals of a number of other countries among the workers feared slain by Islamist gunmen, the siege at a gas field in the Algerian desert has catapulted security in Africa's Sahel region to the top of the international agenda."
1722 GMT: Meanwhile AFP publishes its first photos of the In Amenas site as a photographer finally arrives at the site -- after a gruelling journey which took almost three days.
Eric Baradat, AFP photo editor in chief based in Paris, tweets @Ebaradat: "Finally! First pictures from AFP photog Farouk Batiche in In Amenas coming in!! Took him over 60h to drive there."
1717 GMT: One of the freed hostages speaking on Algerian state television identifies himself as Briton Darren Matthews.
He too says he is "very relieved" to be out and returning to friends and family, adding: "I feel safe at the moment but I won't feel 100-percent happy until I'm back in the UK, until I see my family... but my heart goes out to the guys that are stil there and hopefully everyone comes home safe."
1704 GMT: A Scottish hostage interviewed on Algerian TV says he is "very relieved to be out".
"We still don't know really what's happening back on site so as much as we're glad to be out our thoughts are with colleagues who are still there at the moment," he says.
And he adds his voice to a chorus of praise for the "fantastic" Algerian army from the released hostages, adding: "I've never been so relieved as when they came and got us off site."
1653 GMT: Algerian state television has broadcast some of the first images of the freed hostages, including the two interviews we brought you previously.
Some of those released were being treated in hospital for their wounds. One, who appeared to be seriously injured, said: "It happened so fast" as he struggled to recall details of when the attack began. One of those injured had bandages around his head and said he was from the Philippines.
1623 GMT: Freed British hostages, speaking on Algerian television, say they were impressed by the Algerian army's handling of the situation and appeared unfazed by their experiences.
"I think they did a fantastic job," one man said. "I was very impressed with the Algerian army...very exciting episode... I feel sorry for anybody who's been hurt; but other than that I enjoyed it.
Another added: "I thought the army and the gendarmes have done fantastic jobs -- kept us all nice and safe and fought off the bad guys. I never really felt in any danger to be honest."
1604 GMT: Speaking on condition of anonymity, a US official tells AFP: "This situation is ongoing and sensitive and our top priority at this point is the security of the hostages."
Other officials said the US government was in constant contact with the Algerian government. President Obama spoke to the British PM Friday but has refrained from commenting himself on the situation.
1555 GMT: The latest toll from APS news agency: 670 hostages have been freed, among them 573 Algerians and around 100 foreigners. Algerian special forces are still searching for 30 hostages who are still missing.
"Around 100 foreigners out of 132 hostages seized by a terrorist group that attacked the Tiguentourine gas plant on Wednesday have been freed," APS reported, citing a security official.
1546 GMT: Norway is still struggling to get the green light from Algiers to send two air ambulances to the hostage site. A commercial SAS aircraft which has been converted into a medical plane has left Norway and was expected to reach Algiers Friday afternoon.
But foreign ministry spokesman Frode Andersen told AFP the plane was being blocked from accessing the site itself, saying: "For the moment, we haven't been authorised to land at In Amenas."
1538 GMT: 100 FOREIGN HOSTAGES FREED, 30 STILL MISSING: APS
1535 GMT: ALGERIA HOSTAGE SITUATION STILL 'ONGOING' AND 'SENSITIVE': US OFFICIAL.
1533 GMT: Britain's Foreign Office, which earlier told AFP it had sent a consular team to eastern Algeria, posts on Twitter: "9 consular staff and a 6 person Red Cross psychosocial support team travelled to Algeria today to join the 5 consular staff already there."
In his speech to parliament earlier PM David Cameron said: "We are liasing closely on BP's evacuation plans and have put additional civilian aicraft on stand by to assist them with their well thought evacuation plan if needed."
1525 GMT: In case you're just joining us, here's a quick recap on the latest developments in the hostage situation:
-- 650 hostages have been freed, including 70 foreigners, while 60 foreigners are still missing, according to Algeria's APS news agency.
-- The hostage-takers have said they want to negotiate an end to the situation, the ANI agency reported. The al Qaeda-linked militants want an end to French intervention in Mali and swap American hostages they are holding for Islamist prisoners held in the US.
-- France is standing firm on its position in Mali, with French President Francois Hollande saying the Algeria situation provided "even more justification" for his intervention in the west African country.
-- Security sources told AFP that 18 hostage-takers had been killed at the plant while the British PM said Algerian soldiers were still pursuing "terrorists" holed up in the facility.
1511 GMT: ANI reported earlier that Islamist leader Belmokhtar was proposing an exchange of American hostages held by his group (the 'Signatories in Blood')" for Egyptian Omar Abdul Rahman and Pakistani Aafia Siddiqui, jailed in the US on terrorism charges.
Abdul Rahman, the spiritual leader of the radical Jamaa Islamiya group, was convicted in 1995 for his role in a 1993 attack on the World Trade Centre in New York, in which six people died.
He is serving a life sentence for the attack in which hundreds more people were injured when a truck bomb was detonated in the building's garage. Known as the "blind sheikh," he was also convicted of plotting to bomb other NY targets including the UN and plotting to assassinate ousted Egyptian president Hosni Mubarak.
1503 GMT: Algeria has drawn criticism from some foreign governments for its handling of the situation – Japan, for example, has summoned the Algerian ambassador.
But US-based global intelligence group Stratfor argues its response must be seen in the context of Algeria’s wider struggle against Islamist militants, particularly after France’s intervention in Mali.
"While Algiers has pledged some cooperation, it will not defer to the West for its national security," Stratfor said in an analysis of the situation.
"(The operation) was designed to deter future militant kidnapping operations, and as a result, jihadists now recognize that Algiers did not negotiate or offer ransom payments."
1457 GMT: Some 60 foreigners are still missing, APS reports, after saying earlier that 650 hostages, including 70 foreigners, had been freed.
The agency says the final number of foreigners who managed to escape from the kidnappers is unavailable, as some were still either in hiding or being held hostage inside the industrial complex.
The In Amenas plant, jointly operated by BP, Statoil and Sonatrach, has been put out of service to avoid the risk of explosion.
1446 GMT: More accounts are emerging from hostages who have escaped or been freed since the assault began on Wednesday.
One Algerian engineer describes the moment before dawn on Wednesday when he realised the plant was under attack from Islamist gunmen. He says: "There were gunshots, explosions and an alarm went off. Just after, everything went dark. They cut the electricity and started going through the rooms, smashing down doors when they had to."
He said the kidnappers stalked the site looking for foreigners.
"All the time they were shouting that they were only after expats: 'if you're Algerian you can go, get your stuff and get out!'
"They rounded up all the expats, tied them up and took them off."
1432 GMT: The International Energy Agency (IEA) earlier warned that the hostage-taking could have serious consequences for Algeria's energy sector as Islamists threatened further attacks.
"The 16 January kidnapping and murder of foreign oil workers at the In Amenas gas field has cast a dark cloud over the outlook for the country's energy sector," the IEA said.
"Production at the field was shut in, including an estimated 50,000 barrels per day of condensate."
1418 GMT: ANI is reporting that the hostage-takers want to negotiate an end to French intervention in Mali and exchange American hostages for prisoners held in the United States.
Sources close to their leader, Mokhtar Belmokhtar, say he has proposed that France and Algeria negotiate "an end to the war being waged by France in Azawad" (northern Mali), the news agency says.
In a video message Belmokhtar proposes "exchanging American hostages held by his group (the 'Signatories in Blood') for Egyptian Omar Abdelrahman and Pakistani Afiah Sidiqi, jailed in the United States on charges of terrorist links".
1411 GMT: Algerian troops are still trying to free an unknown number of foreigners held in different parts of the complex, APS reports.
"(The army) is trying to reach a peaceful solution before neutralising the terrorist group that is holed up in the plant and freeing a group of hostages still being held there," the official state news agency said.
1400 GMT: Britain has sent a Boeing 757 with a FCO consular team on board, including trauma experts, which has landed in the last hour in Hassi Messaoud in eastern Algeria, some 280 miles from the hostage site.
"It has landed in the last hour. It has a rapid deployment team onboard including experts in dealing with people who've been through traumatic situations. They are on standby if needed," a Foreign Office spokesman said.
He refused to speculate about who else might be on board, or whether it might be used to bring back British hostages.
1350 GMT: More on that breaking news from Algeria's APS news agency which reports: "Nearly 650 hostages seized in the attack carried out on Wednesday by a terrorist group at the In Amenas gas complex, among them 573 Algerians and more than half of the 132 foreign hostages, were freed."
1345 GMT: GUNMEN WANT TO EXCHANGE ALGERIA HOSTAGES FOR PRISONERS IN US: AGENCY.
1341 GMT: ALGERIA HOSTAGE-TAKERS WANT TO NEGOTIATE END TO MALI INTERVENTION: AGENCY.
1335 GMT: NEARLY 650 HOSTAGES FREED BY ALGERIAN ARMY, INCLUDING AROUND 70 FOREIGNERS: APS
1327 GMT: Interestingly, the French foreign ministry spokesman also distanced himself from criticisms of the Algerian military operation from countries including Japan and Britain.
"The Algerian authorities judged that they had no other choice but to launch an assault," Lalliot said.
"The situation was particularly complex given the scale of the hostage taking and it is still very confused."
1317 GMT: Worth remembering that the attack claimed by Mokhtar Belmokhtar, the one-eyed jihadist with Al-Qaeda links, is thought to be in retaliation for France's intervention in Mali.
In a strident defence, French President Francois Hollande said Thursday that the situation in Algeria "provides even more justification for the decision I took in the name of France to come to the aid of Mali."
1310 GMT: France, which is leading military action in neighbouring Mali, says the Algeria crisis is a wake-up call for the world on the regional situation.
"What's happening in Algeria shows what is at stake for the entire international community with the presence of terrorist groups in this zone," foreign ministry spokesman Philippe Lalliot said.
1301 GMT: Norway also says it's working with Algerian authorities to get permission to dispatch an air ambulance to the area. The aircraft is currently parked in Sicily and must remain at least 500 km (310 miles) away from the hostage site.
Norwegian oil and gas company Statoil, one of the company's which operates the facility, said earlier that another one of its Norwegian employees had been taken to safety while the fate of eight others is still unknown.
1256 GMT: ALGERIA CRISIS SHOWS WORLD MUST ACT ON SAHEL EXTREMISTS: PARIS.
1250 GMT: Algeria continues to come in for criticism over its failure to communicate its operational plans, with Norway saying it would have prefered to have been informed before it happened, echoing similiar comments by the British PM earlier.
"We have indicated that we would have liked to be informed in advance," Foreign Minister Espen Barth Eide told the news channel TV2 Nyhetskanalen as eight Norwegians remained unaccounted for.
As with Cameron, the Norwegian minister stopped short of criticising the Algerian government, however, adding that it was "too early to pass judgement on the operation."
1242 GMT: US Defense Secretary Panetta is due to meet British PM Cameron for talks at Downing Street later Friday to discuss issues including the situation in Algeria.
Cameron was due in the Netherlands to give a key speech on Europe today but this has been postponed amid the crisis. The Panetta talks are thought to have been arranged after that.
1235 GMT: Here's a quick recap of some of the latest developments in the ongoing crisis:
-- Hostages are still being held at the remote In Almenas gas facility where the Algerian army is pursuing "terrorists" and searching for those missing, British Prime Minister David Cameron said.
-- The precise details of the situation remain cloudy, but one security source says 18 hostage-takers have been killed at the gas plant, while others are still "holed up" in the plant.
-- Algeria says a "large number" of hostages have been freed in its military rescue operation, but reports say that while 600 locals were released, only a handful of the 41 foreigners were freed.
-- BP, which operates the gas facility, says hundreds of people have been evacuated in a "staged process" to bring non-essential workers out of Algeria.
-- Details have been filtering through of what happened when Islamists attacked the site on Wednesday, including reports from a freed hostage that gunmen attached explosives to foreign hostages. Cameron said Algeria intervened because there was "an immediate threat to the lives of the hostages".
1217 GMT: Scotland's First Minister Alex Salmond says a number of Scottish residents who had been held captive in Algeria have been confirmed as "safe and well".
1213 GMT: "Those who would wantonly attack our country and our people will have no place to hide," US Defense Secretary Leon Panetta says in a speech in London.
He says Washington is working to secure the safe return of an unknown number of Americans who had been at the plant.
1209 GMT: TERRORISTS WHO ATTACK US INTERESTS HAVE NO PLACE TO HIDE: PANETTA.
1204 GMT: Eighteen kidnappers were killed on Thursday in an assault launched by the Algerian army at the In Amenas gas complex to free hundreds of hostages held there, an Algerian security source says.
"Eighteen terrorists were killed yesterday," the source told AFP, adding that the Islamist gunmen who had carried out the hostage-taking operation at the remote site in southeast Algeria numbered more than 30.
1157 GMT: Earlier British Prime Minister David Cameron made it clear that Algerian troops are stil pursuing gunmen at the under-siege site and searching for hostages.
Cameron told parliament the first stage of the military operation was complete, "but this is a large and complex site and they are still pursuing terrorists and possibly some of the hostages in other areas of the site".
1153 GMT: The Islamists hostage-takers have threatened to stage more attacks, according to a spokesman cited by the Mauritanian news agency.
"Taking into account the suffering of the Algerian people, we promise the regime in place that there will be more operations," a spokesman for the "Signatories in Blood" told ANI.
He asked Algerians to "clear out from sites belonging to foreign firms (as) we will emerge in places where nobody is expecting us."
Veteran Islamist fighter Mokhtar Belmokhtar, a one-eyed Algerian jihadist with Al-Qaeda ties, has claimed responsibility for Wednesday's attack on the In Amena complex.
1147 GMT: 18 HOSTAGE-TAKERS KILLED AT ALGERIA GAS PLANT: SECURITY SOURCE.
1145 GMT: Both Downing Street (@Number10gov) and Britain's Foreign Office (@foreignoffice) are aggressively pushing out their lines on this crisis through Twitter.
Apparently keen to establish a clear narrative, Downing Street quickly followed up Cameron’s statement to parliament with a restatement of several key lines which are getting retweeted around the world.
1137 GMT: The British PM reiterates his comments on Twitter @Number10gov: "We need to be absolutely clear whose fault this is -- it is the terrorists who are responsable."
A few moments ago he told parliament: "The actions of these etxremists can never be justified. We will be resolute in our determination to fight terrorism and to stand with the Algerian governement who have paid a heavy price over many years fighting agaisnt a salvage terrorist campaign."
1132 GMT: Meanwhile US Defense Secretary Leon Panetta, on a visit to London, says there is "no justification for the kidnapping and murder of innocent people" in Algeria, adding the US is "working around the clock to ensure the safe return of our citizens".
1127 GMT: Cameron says two of those travelling in the convoy to the airfield on Wednesday were killed, including one British national.
"A number of other workers were taken hostage by the terrorists in separate locations both at the residential compound and at the gas facility," he says.
"The precise numbers involved remain unclear at this stage but the hostages included British nationals along with the nationals of at least seven other coutnries and of course many Algerians."
1121 GMT: More on that statement from David Cameron... He says the militants attacked two buses en route to the facility before launching their attack on the residential compound and gas facility in In Amenas, which he describes as "one of the most remote places in the world".
"It appears to have been a large well-coordinated and heavily armed asssault and it is probable that it had been pre-planned," he says.
1110 GMT: British Prime Minister David Cameron says less than 30 British hostages were at risk last night but that number has "quite significantly reduced".
In a statement in the House of Commons he said the Algerian government had not informed Britain in advance of the rescue operation but pledged to stand by the Algerian government and firmly placed the blame on the "terrorists".
1102 GMT: HUNDREDS EVACUATED FROM ALGERIA: BP says it began a "staged process" overnight to bring non-essential workers out of Algeria as a "precautionary and temporary measure".
"Three flights left Algeria yesterday, carrying a total of eleven BP employees alongside several hundred staff from other companies," BP's statement says.
"The first flight arrived in London yesterday afternoon. The second two flights landed in Palma in Majorca overnight and staff on these planes are expected to transfer on to final destinations during the course of the day.
"A fourth plane is expected to transport further staff out of the countrytoday and we will arrange further flights as necessary."
1057 GMT: BP, which operates the besieged gas facility, has released a statement saying the "serious situation" in In Amenas "remains ongoing".
"The situation remains unclear and BP continues to seek updates from the authorities," a statement from the British company said.
"There is a small number of BP employees at In Amenas whose current location and situation remain uncertain. BP is working with the Algerian government and authorities to confirm their status. We do not intend to publicly comment on details of the number, nationalities or identities of these staff."
The company said it was in direct contact with the families of all of those staff affected. BP's group chief executive added: "Supporting our colleagues and their families at a time of such extreme concern is essential, and we are seeking to support them in every way we can."
1050 GMT: Nick Butler, a former head of strategy for BP who is now a visiting fellow at King's College London, tells BBC radio that energy companies would now be assessing their future operations in the region amid fears that conflict could spread.
"I think the real concern now is that what happened yesterday, whatever the detail was, could lead to more reprisals and that one incident leads to the next in revenge," he says. "That will make the companies look very hard now at the number of staff they have there, at the operations they have and at the level of security.
"The impression was that the country was getting better... now it could deteriorate, there's obviously the risk of people coming over the border, the defeated Libyan opposition, the defeated people from Mali. All those borders around there are very porous and the risk of conflict spreading is quite serious."
1045 GMT: A security source says the militants' claim of dozens of people killed in the army rescue bid is "fantasy".
Speaking to AFP, the source condemned the Mauritanian news agency ANI, to which the Islamists gave their account of events on Thursday, claiming 34 captives and 14 hostage-takers had been killed.
"The terrorists made contact with ANI to give them this exclusive report, from which we got this fantasy toll," he said.
1037 GMT: More from escaped hostage Berceaux... "Nobody expected this," he says. "The site was protected. There were soldiers in place.
"I stayed hidden for nearly 40 hours in my room. I was under the bed and I put boards everywhere just in case. I had a bit of food, a bit to drink, I didn't know how long it would last."
He said three Englishmen who had hidden above a dropped ceiling were also rescued, adding: "I think there are still people hidden. They are in the process of doing a count now."
1032 GMT: A French national says he hid under his bed for 40 hours during the hostage-taking before being rescued by soldiers during an assault that involved heavy exchanges of gunfire.
Alexandre Berceaux, an employee of CIS Catering at the desert gas complex who was evacuated to another nearby site, also told Europe 1 radio that the initial attack on the site was a surprise as the base was heavily guarded.
He said "there were intervals of heavy gunfire" when Algerian forces stormed the base Thursday, adding: "There are terrorists who are dead, expatriates, locals".
"I heard an enormous amount of gunfire. The alarm telling us to stay where we were was going off. I didn't know if it was a drill or if it was real."
1025 GMT: As pressure mounts on Algeria over its handling of the situation, new details have emerged about the Algerian rescue operation -- including reports that hostages had explosives strapped to them.
Irish foreign minister Eamon Gilmore says some of the hostages came under fire as Algerian authorities intervened when the al Qaeda-linked kidnappers attempted to move their captives. He was speaking after 36-year-old father of two, Stephen McFaul, from Belfast in Northern Ireland escaped from the facility.
"I have been told at the stage where they were being transported explosives were strapped to them,” Gilmore told CNN after speaking to McFaul's wife Angela by phone.
"The information that I have is that there were five vehicles involved; four of those vehicles were hit. The vehicle in which Stephen McFaul was not hit and he managed to get away, but as I said it’s still at a very early stage and we’re still assembling the information."
1013 GMT: DEATH TOLL GIVEN BY HOSTAGE-TAKERS 'FANTASY': SECURITY SOURCE.
1008 GMT: Some Islamist gunmen are still holed up at the remote Algerian gas field, a security source says.
"There is still a group holed up" at the In Amenas gas production complex in the southeast desert, the source tells AFP, adding that it was "difficult to discuss an ongoing operation."
1000: GMT: SOME ALGERIA HOSTAGE-TAKERS 'STILL HOLED UP' IN GAS COMPLEX: SECURITY SOURCE.
0956 GMT: Eight Norwegians are still unaccounted for in the siege at the BP-operated facility, while one appears to have escaped, Norway's Foreign Minister Espen Barth Eide says.
"At this moment we have eight hostages, eight people who are unaccounted for in the situation," Eide told BBC radio.
"This morning we got news that the ninth person is actually free and is at a local hospital in In Amenas."
Four other Norwegian nationals had "got out at an early stage", he added.
0949 GMT: Some 34 Filipinos working at the gas field have been flown out of the country, a Philippine government spokesman says.
Another Filipino worker escaped on his own along with a Japanese national, Foreign Undersecretary Raul Hernandez said. Of those evacuated and flown to London on Thursday, one had suffered a gunshot wound, he added, declining to confirm reports that at least two Filipinos were among those killed in the Algerian rescue operation.
"The Algerians admitted that there were some deaths and injuries on the side of the hostages following the operation undertaken by the Algerian military forces but no details were released," Hernandez said.
0941 GMT: Several world leaders made changes to their schedules today, reflecting their growing concern about the hostages' fate. Prime Minister David Cameron has cancelled a key speech on Britain's relationship with the EU in the Netherlands while Japan's Prime Minister Shinzo Abe cut short a visit to Indonesia.
Japanese plant builder JGC has confirmed the safety of three of its Japanese staff and one Filipino employee, but the whereabouts of 74 other staff, 14 of them Japanese, remain unknown.
0934 GMT: The Islamist kidnappers say 34 captives have died in the assault, but this is impossible to confirm. So far only the British government has announced a casualty, though it is feared that the toll could be considerably higher.
The militants told Mauritanian news agency ANI they would "kill all the hostages if the Algerian forces succeed in entering the complex".
0924 GMT: Algeria is coming under mounting international criticism over the crisis as dozens of foreign hostages remain unaccounted for, with many feared dead, despite an Algerian military rescue bid.
Japan's foreign ministry has today summoned the Algerian ambassador, demanding answers over the rescue operation. The plant employs workers from Japan, Britain, France, Italy, Norway and the United States.
Japanese senior vice foreign minister Shunichi Suzuki told ambassador Sid Ali Ketrandji that Japan was disturbed by the way the ground and air assault had been carried out, a foreign ministry statement said.
"From the view point of protecting the lives of the hostages, Japan is deeply worried that the government of Algeria conducted the military operation to rescue hostages," Suzuki told Ketrandji, according to the statement.
0918 GMT: While only one British person has been confirmed dead, media reports said as many as 20 Britons may be unaccounted for at the BP-operated In Amenas plant.
One man from Northern Ireland meanwhile managed to escape from the facility and is expected to be returning home to Belfast Friday.
0911 GMT: Britain's Foreign Office says the "terrorist incident" in Algeria is ongoing and confirmed that one Britain had been killed.
Prime Minister David Cameron will later hold a meeting of Britain's COBRA emergency committee after warning of the likelihood of more bad news to come.
"The terrorist incident in Algeria remains ongoing," said a Foreign Office spokeswoman. "As the prime minister and foreign secretary have said, to the best of our knowledge on the information given to us by the Algerian government one British national has sadly been killed.
"We are not in a position to give further information at this time. But the prime minister has advised we should be prepared for bad news."
WELCOME TO AFP'S LIVE REPORT on the Algeria hostage crisis as it enters its third day. Western governments have voiced alarm over the fate of dozens of foreigners seized by Islamists at the In Amenas gas plant in the Algerian desert after several hostages were killed in a dramatic rescue operation.
Here are some of the latest key developments in what Britain described early Friday as an ongoing "terrorist incident".
-- An Algerian military operation aimed at freeing the hostages has left "several people" killed or wounded but freed a "large number" of hostages, an Algerian minister said.
-- Special forces have taken control of a residential compound at the complex wherehundreds of hostages are being held after Islamist militants took control of the gas plant on Wednesday.
-- Algerian soldiers continue to surround the site's main gas facility which they have so far failed to secure in an air and ground assault. Some 600 local workers were however freed Thursday, including two from Britain, one from France and one from Pakistan.