A number of US troops have been killed in a reported suicide bomb attack in Syria claimed by the Islamic State group, the US military says.
IS said one of its militants detonated an explosive vest next to a US patrol in the Kurdish-held town of Manbij.
A Kurdish news agency reported that three US soldiers, two local security officers and 13 civilians died.
US forces are in Manbij to back Kurdish and Arab fighters who have driven IS out of almost all of eastern Syria.
Wednesday’s attack took place at a restaurant near Manbij’s main market.
A witness told Reuters news agency that the US troops were at the restaurant to meet members of the local Manbij Military Council (MMC).
CCTV footage from a nearby shop showed a large fireball engulfing several people standing on the street outside.
The Syrian Kurdish Hawar News Agency (ANHA) reported that the US soldiers were subsequently evacuated by a helicopter that landed on a playground.
It cited the head of Manbij’s health committee as saying that 18 people were killed, including three of the soldiers, and that another 18 were wounded.
Later, a spokesperson for the US-led multinational coalition against IS tweeted: “U.S. service members were killed during an explosion while conducting a routine patrol in Syria today.”
“We are still gathering information and will share additional details at a later time.”
Reuters cited a US official as saying four soldiers died and three were wounded.
Last month, President Donald Trump announced that the US would begin pulling out all its 2,000 troops from Syria because IS had been “defeated”.
Opponents of the withdrawal stressed that although IS now controlled only 1% of the territory they overran five years ago, the group had not disappeared entirely.
A recent US report said there were still as many as 14,000 IS militants in Syria and even more in neighbouring Iraq – and that they were expected to shift to guerrilla tactics in an attempt to rebuild their network.
Syrian Kurds also fear that Manbij and other towns they control near the border with Turkey might come under attack by the Turkish military, which wants to clear them of the Kurdish People’s Protection Units (YPG) militia.
The Turkish government considers the YPG an extension of the banned Kurdistan Workers’ Party (PKK), which has fought for Kurdish autonomy in Turkey for three decades. However, it denies any direct organisational links to the group.