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, reports Reuters.
The attack happened on the western edge of Shadadi town in Hasaka province near a route frequented by the US-led coalition fighting Daesh.
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.
Daesh-affiliated Amaq news agency said a suicide bomber hit a joint US-SDF convoy but did not mention casualties.
The SDF said there had only been material damage, but acknowledged the ultra-hardline militants were expanding attacks, calling them post-defeat phase tactics after being driven out of most territory they once controlled in Syria.
"The intensifying of these terrorist attacks and moving sleeping cells to strike will not dissuade us from completing the mission to the end," the SDF statement said.
Footage on social media showed a burnt-out military vehicle with metal pieces scattered near the checkpoint.
Residents say there has been a spike in recent months in attacks on SDF checkpoints in the swathe of the territory it controls in northeast Syria on the border with Turkey, down the Euphrates River towards the border with Iraq.
Four US citizens died in an Daesh-claimed bombing last week in Manbij city, run by the SDF which is spearheaded by the Syrian Kurdish YPG militia.
Resentment is mounting against the SDF by the predominately Arab population in the vast areas of eastern Syria they rule, with many objecting to compulsory conscription of youths and discrimination in top leadership layers, residents say.
There has been a spate of assassinations of SDF fighters and commanders in recent months, residents say.
The powerful YPG, an important partner in the US-led war against Daesh, is fighting to clear the militants from their last footholds east of the Euphrates River following last year's defeat of the group in Raqqa, its Syrian headquarters.