BEIRUT (AP) -- U.S.-led coalition strikes targeted Islamic State group positions overnight across in northern and eastern Syria, including one that hit a grain silo and reportedly killed civilians, activists said Monday.

Washington and its Arab allies opened their air assault against the extremist group last week, going after its military facilities, training camps, heavy weapons and oil installations. The campaign expands upon the airstrikes the United States has been conducting against the militants in Iraq since early August.

The Britain-based Syrian Observatory for Human Rights said coalition forces hit Islamic State group facilities overnight in Aleppo, Raqqa, Hassakeh and Deir el-Zour provinces. It said there were casualties, including civilians, but that it did not have concrete figures.

One of the strikes hit a grain silo in the extremist-held town of Manbij in Aleppo province, setting it ablaze, the Observatory and the Aleppo Media Center activist group said. Another activist collective, the Local Coordination Committees, also reported what it said were coalition air raids on Manbij.

Observatory director Rami Abdurrahman said the strike on the grain silo killed civilians, but he didn't have an exact figure.

“They killed only civilians there, workers at the site. There was no ISIS inside,'' he said, using an alternative name for the Islamic State group. The airstrikes “destroyed the food that was stored there.''

There was no immediate comment or confirmation of the strikes from the U.S. or its allies.

In Deir el-Zour province, a strike overnight attributed to the coalition hit the entrance to the Conoco gas plan, Syria's largest, according to the Observatory.  It said the gas facility itself was not damaged.

More raids Monday morning struck the town of Tel Abyad on the Syria-Turkey border, according to a resident on the Turkish side on the frontier.