Twin explosions in the Philippine capital on Saturday night killed two people and injured six others, police said, just over a week after another blast in the same area.
Authorities initially said there were no indications the blasts were terrorist attacks but the Islamic State (IS) group claimed responsibility.
The militants cited a higher death toll than that given by police and said it was a sectarian strike against Shiite Muslims.
"Five Shiites were killed and six others wounded in a bomb blast by Islamic State fighters in the centre of Manila in the Philippines," IS propaganda outfit Amaq said in a statement.
The initial blast occurred around 6:00pm (1000 GMT) near a mosque in Quiapo, one of the older parts of Manila where there are big slums, city police chief Oscar Albayalde said.
The explosion killed two and injured four others, he said.
A second blast occurred in the same area around 8:30pm, according to an AFP photographer who was among a group of journalists near the scene.
Two policemen who were inspecting the area after the first blast were injured by the second explosion, Albayalde said in an interview on GMA television.
The blasts occurred along a narrow street crammed with stalls hawking clothes and homeware.
They were just outside an Islamic community centre and about a hundred metres (300 feet) from the Quiapo Golden Mosque.
The Philippines is a mainly Catholic country but it has a significant Muslim minority, some of whom live in Quiapo.
The first blast damaged part of the Islamic centre and shattered windows in nearby buildings, according to the AFP photographer and witnesses.
"It was very powerful," Omar Yahya, 22, who was at the Islamic centre when the first explosion occurred, told AFP afterwards at a Manila police station.
"Windows were broken and the wooden part of the building collapsed."
- 'No sign of terror attack' -
Police chief Albayalde said the first blast appeared to have come from a package that was being delivered by a man on a motorcycle.
"The man on the motorcycle who delivered the package was killed. The other killed was the person who received the package," he said in an interview on DZRH radio.
Albayalde said there was no signs that the blasts were terrorist attacks.
"We do not want to speculate but it's possible this is a gang war," he said.
"We do not see any indication that this is a terror attack."
The other explosion in Quiapo just over a week ago, which occurred as Southeast Asian leaders were meeting for a summit a few kilometres (miles) away, injured 14 people.
IS claimed responsibility for the April 28 explosion, but police insisted it was not a terrorist attack, nor was it related in any way to the gathering of political leaders.
Police said the April 28 explosion involved a home-made pipe bomb and was carried out by people involved in a private grievance. They said one person had been arrested over that attack.
Militants who have pledged allegiance to IS are based in the southern Philippines, more than 800 kilometres (500 miles) from Manila.
Those militants mainly operate in the south, although they have been blamed for terrorists attacks in Manila.
The Abu Sayyaf group, which is most infamous for kidnapping foreigners and killing them if ransoms are not paid, was blamed for the bombing of a ferry in Manila Bay in 2004 that killed 116 people.