DAMASCUS, Sept. 25 (Xinhua) -- U.S.-led airstrikes at the Islamic State (IS) group's Syrian stronghold Raqqa in March killed at least 84 civilians, including dozens of children, Human Rights Watch (HRW) said Monday.

The organization said the strikes hit two sites: a school housing displaced families in the town of Mansourah, and a market and bakery in the town of Tabqa.

It said witnesses acknowledged that IS fighters had been present at both sites, but that large numbers of civilians were also there.

"These attacks killed dozens of civilians, including children, who had sought shelter in a school or were lining up to buy bread at a bakery," HRW deputy emergencies director Ole Solvang said.

The HRW said the first of the two strikes was on March 20, and killed at least 40 people including 16 children at the Badia School in Mansourah. The second was on March 22 and killed at least 44 people including 14 children at the Tabqa market and bakery.

The U.S.-led coalition has been carrying out airstrikes in support of anti-IS operations in Syria since September 2014, after expanding its existing campaign in neighboring Iraq.