A suicide bomber drove his car into a checkpoint in northeastern Syria on Monday, injuring several soldiers of Kurdish-led forces during a joint convoy with US allies, locals said.
The attack happened on the western edge of Shadadi town in Hasaka province near a route frequented by the US-led coalition fighting Islamic State, residents and sources said.
In a tweet, the coalition said a convoy with allied Kurdish-led Syrian Democratic Forces (SDF) was involved in an attack, but there were no American casualties.
Coalition planes flew overhead after the blast around 11 a.m., a Syria-based aid agency worker said, adding that colleagues had reported several casualties including Kurdish soldiers, coalition troops and civilians.
Four US citizens died in an Islamic State-claimed bombing last week in Manbij city, run by the SDF which is spearheaded by the Syrian Kurdish YPG militia.
Residents say there has been a spike in recent months in attacks on SDF checkpoints in the swathe of territory it controls in northeast Syria on the border with Turkey, down the Euphrates River towards the border with Iraq.
The powerful YPG, an important partner in the US-led war against Islamic State, is fighting to clear Islamic State from its last footholds east of the Euphrates River following last year's defeat of the group in Raqqa, its Syrian headquarters.