ISTANBUL (REUTERS) - A bomb attack claimed by Islamic State in Iraq and Syria (ISIS) killed US troops in northern Syria on Wednesday (Jan 16), weeks after President Donald Trump said the group had been defeated there and that he would pull out all American forces.
A US official who declined to be named said four US troops had been killed and three wounded in the blast, which an ISIS-affiliated site said was the work of a suicide bomber.
A war monitor said 19 people in total had died in the blast.
The US-led coalition fighting the Islamist militant group said that "US service members were killed during an explosion while conducting a routine patrol", and that it was still gathering details.
The attack, which took place in the town of Manbij, controlled by a militia allied to US-backed Kurdish forces, appears to be the deadliest on US forces in Syria since they deployed on the ground there in 2015.
A Pentagon spokeswoman said that only two US troops had previously been killed in action in Syria. There were two additional non-combat fatalities.
Last month, Trump made a surprise announcement that he would withdraw all 2,000 US troops from Syria after concluding that ISIS had been defeated there.
The announcement helped trigger the resignation of his defence secretary, Jim Mattis, stunned allies and raised fears of a long-threatened Turkish military offensive against US-backed Kurdish forces in northern Syria.
Turkish President Tayyip Erdogan said he did not believe the attack would impact the US decision to withdraw from Syria "because I saw honourable Trump's determination on this point".
Speaking at a news conference in Ankara, Erdogan said his information suggested that five US troops had been killed in the Manbij attack.
How, and how quickly, US forces pull out has caused ructions in northern Syria, with both Turkey and the Syrian government of President Bashar al-Assad ready to fill the vacuum.
The US-backed YPG militia that is allied to the fighters holding Manbij last month invited Assad into the area around the town to forestall a potential Turkish assault. Syrian army troops entered the area soon after.
A witness in Manbij said Wednesday's attack had targeted a restaurant where US personnel were meeting members of the local militia backed by Washington.
The Syrian Observatory for Human Rights monitoring group said 19 people had been killed in all, including four Americans. A militia source in north Syria said two US troops had been killed.
ISIS later put out a statement saying a Syrian fighter had detonated his explosive vest on a foreign patrol in Manbij.
Two witnesses described the blast to Reuters.
"An explosion hit near a restaurant, targeting the Americans, and there were some forces from the Manbij Military Council with them," one said.
The Manbij Military Council militia has controlled the town since US-backed Kurdish-led forces took it from ISIS in 2016. It is located near areas held by Russian-backed Syrian government forces and by anti-Assad fighters backed by Turkey.
One of the witnesses said there was a "heavy" presence of military aircraft over Manbij following the blast, which took place near a vegetable market.
Photographs on a local Kurdish news site, which Reuters could not verify, showed two mutilated bodies, several other bodies lying on the ground with people gathered around them, damage to a building and vehicles, and blood smears on a wall.
It was unclear whether the attack might influence Trump's decision to give more time for the US withdrawal, a conflict he has tired of and described as "sand and death".
Now in its eighth year, Syria's war has killed half a million people, forced more than half the country's pre-war population from their homes and dragged in global and regional powers.
Assad now controls most of the country, but Kurdish-led forces backed by the United States hold more than a quarter of Syria and rebels have a last enclave, divided between jihadist insurgents and Turkey-backed fighters, in the north-west.