U.S.-led coalition warplanes have bombed Islamic State positions across northern and eastern Syria.
The Britain-based Syrian Observatory for Human Rights said on September 29 that coalition aircraft hit targets in four provinces: Aleppo, Raqqa, Hassakeh, and Deir el-Zour.
The activist group said the strikes hit grain mills and silos in the extremist-held northern town of Manbij by mistake after apparently assuming they were a militant base.
There was no immediate comment from Washington.
The activist group also reported that the strikes hit the entrance to Syria's largest gas plant, Conoco, in Deir el-Zour Province.
Washington and its Arab allies opened their air assault against the extremist group last week.
The campaign expands upon the air strikes the United States has been conducting against the militants in Iraq since early August.