Air strikes by a U.S.-led coalition fighting to oust the Islamic State extremist group from its stronghold of Raqqa killed at least 29 Syrian civilians, including 14 children, in 24 hours, a war monitor said on August 8.
The dead include a family of 14, the Syrian Observatory for Human Rights said.
The U.S.-led coalition did not immediately respond to the accusation. The coalition has previously said it makes extraordinary efforts to avoid killing civilians and investigates all reports of such casualties.
The coalition said last month that its strikes had killed at least 600 civilians in Iraq and Syria since it began operations in 2014. Rights groups say the total is much higher.
The Syrian Democratic Forces, an alliance of Syrian Kurds and Arabs, began an assault to retake Raqqa in June.
The U.S.-led coalition has helped the alliance with air strikes and some artillery support, and by supplying arms.
The UN estimates that up to 50,000 civilians are still trapped inside Raqqa amid the fighting.