Dozens of people, including children, are feared to have been killed and more wounded in two explosions at Kabul airport, where thousands of people had gathered to try to flee the country.
Isis admitted carrying out the attacks, which killed at least 12 US service members, including 11 Marines and one Navy medic, according to two US officials. A number of US military troops were wounded.
At least 60 Afghans were also killed, according to local officials, and video images uploaded by Afghan journalists showed dozens of bodies of people killed in tightly packed crowds outside the airport.
The US general overseeing the evacuation from Afghanistan said the United States would “go after” the perpetrators if they could be found.
Gen Frank McKenzie said the attacks were believed to have been carried out by fighters linked with the Islamic State group’s Afghanistan affiliate.
And Senate majority leader Chuck Schumer said that those responsible “will be sought and brought to justice”.
There were no UK military or government casualties, the Ministry of Defence said, and Boris Johnson, who chaired an emergency Cobr meeting with ministers, insisted the evacuation effort in Kabul would continue despite the “barbaric’’ terrorist attack.
The prime minister said the “overwhelming majority” of eligible people had already been helped to flee the Taliban by the RAF and the UK would “keep going up until the last moment” as the deadline rapidly approached.
The head of the US military’s central command said two suicide bombers were involved.
The blasts followed warnings that a terror attack could be launched in the final phase of the evacuation effort before the Taliban takeover of Afghanistan is complete on Tuesday.
The Taliban condemned the attack, saying it occurred in an area controlled by US forces. Spokesman Zabihullah Mujahid said his group “strongly condemned” it, and was paying close attention to security.
The militant group, which has been trying to control the mass of people at the airport gates, has pledged not to attack Western forces during the evacuation, but insists the foreign troops must be out by America’s self-imposed deadline of Tuesday.
An emergency hospital in Kabul counted at least 60 wounded people, and the US military was reported to be “bracing itself for more attacks”.
US Pentagon spokesman John Kirby said the first explosion was at Abbey Gate, and the second was at the Baron hotel, where the UK has been processing Britons and Afghans eligible for evacuation after the Taliban seized control of the country.
The US embassy in Kabul warned anyone at the Abbey Gate, East Gate or North Gate to leave immediately.
Adam Khan, an Afghan waiting outside the airport, said the first blast went off in a crowd of people waiting to enter the airport. Khan, who was about 30 yards away, said several people appeared to have been killed or wounded, including some who lost body parts.
A former interpreter with UK forces who was with his wife, and two young children waiting for an evacuation flight reportedly said: “It was like doomsday, injured people everywhere”.
Another witness said the first blast was followed by gunfire.
Emergency, a volunteer group that runs war surgery hospitals and first aid posts across Afghanistan, said some people were dead on arrival. “We have activated all mass casualty protocols,” it said.
Thousands of Afghans have been gathered at the airport for days trying to escape from the country since the Taliban takeover earlier this month. Western nations had warned of a possible attack.
A UK government source said final evacuees who have been approved for travel to the UK, along with a few still undergoing security checks at the Baron hotel, were expected to be flown out of Afghanistan by the end of Friday, with the withdrawal of British officials, diplomats and troops expected to be completed by the end of the weekend.
A senior British source said it was now “highly unlikely” that any more people would be admitted into the airport to seek evacuation on RAF flights.
Mr Johnson was briefed at the Cobr meeting on whether the withdrawal should be accelerated in response to the attack, but concluded that this was not necessary as the mission was already close to its end and was being terminated as quickly as possible.
Tom Tugendhat, chair of the foreign affairs select committee, tweeted: “The attack on innocent people at Kabul airport simply trying to escape the horror of Taliban rule shows exactly who the group has brought with them. The pattern is well established - from Nigeria and Mali to Syria and Iraq, whenever Islamist extremists take power, terror follows.”
Tory MP Nus Ghani said she was on the phone to somebody outside Kabul airport when the explosion happened.
The Wealden MP tweeted: “Explosion at Kabul airport. I was on the phone to an Afghan outside the airport when he heard the explosion.
“Praying that he gets away safely and we get his family safe passage out of this nightmare.”
Another Tory MP, Alicia Kearns, tweeted: “A bomb or attack with gun fire at northern gate of Baron’s hotel. Worried this will devastate evacuation - so many hurt. My heart is with all those injured and killed.”
Several countries urged people to avoid the airport earlier in the day, with one saying there was a threat of a suicide bombing. But just days — or even hours for some nations — before the evacuation effort ends, few appeared to heed the call.
Overnight, warnings emerged from Western capitals about a threat from Afghanistan’s Islamic State group affiliate, whose ranks are thought to have been boosted by the Taliban’s freeing of prisoners across the country.
British Armed Forces minister James Heappey told the BBC early on Thursday there was “very, very credible reporting of an imminent attack” at the airport, possibly within hours.
The Ministry of Defence said it was working urgently to establish what happened in Kabul and its effect on the evacuation effort.
“Our primary concern remains the safety of our personnel, British citizens and the citizens of Afghanistan,” a statement added.
The faction of Isis that is active in Afghanistan is called “Wilayah Khorasan” by Isis (Isis-K by others), meaning “Khorasan State”. Its “wilayat” are regional factions in different parts of the world. It covers Afghanistan, Pakistan and other parts of south Asia.
They have fought the Taliban now and again, as well as Afghan forces, and have launched significant terror attacks. They have not claimed any attacks on the Taliban since 14 August but previously did every few days.