A car bomb exploded near a military position in Syria's Raqqa on Sunday, local authorities and a war monitor said, and Islamic State group said it was behind the blast.
The blast came a day after the assassination of a local council leader in the city, the former Syrian capital of the militant group's self-declared caliphate, which was seized a year ago by US-backed Kurdish-led fighters.
Raqqa security forces said a civilian had been killed and several people, including civilians and fighters injured. The war monitor, the Syrian Observatory for Human Rights, said the blast caused "a large number" of casualties.
Islamic State said in a statement that it had detonated the bomb, targeting fighters from the Kurdish YPG militia, the strongest element in the U.S.-backed Syrian Democratic Forces (SDF) group that drove the militants from Raqqa last year.
The SDF is battling Islamic State fighters in one of their last patches of territory in Syria, along the north bank of the Euphrates river close to the Iraqi border.
The militants took advantage of bad weather on Sunday to attack SDF positions, killing a dozen fighters, the Observatory reported.
Syrian state television reported on Sunday that the Syrian army was assaulting the jihadists' other remaining pocket of ground in the desert area in Sweida province in southern Syria.