At least 10 people were killed when an Islamic State suicide bomber blew himself up in a village in northern Syria in the early hours of Tuesday, the Syrian Observatory for Human Rights monitoring group said.
The blast took place in al-Mashi, which is in the countryside around the city of Manbij and wounded another 20 people, it said. U.S.-backed forces captured Manbij and its surrounding areas from Islamic State in August.
The jihadist group is launching attacks against those forces in the Manbij area, the British-based Observatory says.
Since the Manbij operation, a Kurdish contingent of the U.S.-backed Syria Democratic Forces has withdrawn from the city, the Pentagon said last month, but non-Kurdish forces from the SDF-allied Manbij military council remained.
Turkey, which has fought against the Kurdish YPG militia in Syria, is supporting Syrian insurgents in a separate push against Islamic State further west of Manbij.
Al-Mashi is currently under the control of the Manbij Military Council, the Observatory said.