At least 56 civilians were killed Tuesday in new airstrikes by a US-led coalition near the Islamic State-held northern Syrian city of Minbij, a monitoring group said.
At least 11 children were among the dead, the Britain-based Syrian Observatory for Human Rights said, adding that dozens were also wounded.
"We believe that the raids which were carried out Tuesday were by US [or] allied planes, but it was by mistake," Observatory director Rami Abdel-Rahman told dpa.
The Minbij area has seen intense US-led airstrikes in support of Kurdish-led forces who are trying to seize the city from Islamic State so as to block the extremist group's access to the nearby Turkish border.
The Observatory on Monday said that 104 civilians had been killed in airstrikes since the Democratic Forces of Syria (DFS) launched their campaign in the area at the end of May.