At least 5 U.S.-backed forces killed by an improvised explosive device in the eastern province of Raqqa, activists said Monday.
Daesh claimed the responsibility for attack that rocked a bus carrying members in the Syrian Democratic Forces (SDF) in the western countryside of Raqqa.
Aamaq, Daesh news agency, said the attack left 10 SDF fighters dead.
At least 30 SDF fighters were killed in Daesh attacks on their checkpoints in two weeks. The SDF has also killed at least 40 Daesh militants.
On Friday, Daesh militants launched counter attack on the Kurdish-led forces in eastern Deir Ezzor province, killing 8 fighters.
The surprise attack began with a car bomb near the town of al-Hajeen. Three fighters from the SDF were held captive, according to Deir Ezzor-based media activist Taj al-Allow.
Since Tuesday, clashes have intensified between the SDF and Daesh as the YPG-led fighters press to uproot the militants from their last pockets near the Iraqi border.
The fighting near the strategic Bagouz area, key Daesh stronghold in the eastern bank of Euphrates River.
The SDF seized control of the villages of al-Shajlah and Mouzan near the embattled village of Bagouz.
On Wednesday, two US Army soldiers killed along with SDF forces in a car bomb attack in the town of Granij.
Daesh car bomb rocked a joint military patrol, al-Allow said.
Three civilians were also killed in Daesh rocket attack on the SDF-held town of al-Ja’abi.