Health workers pulled little lifeless bodies out from under mounds of rubble after airstrikes reportedly hit and killed 25 children in the eastern part of the Syrian province of Deir Ezzor, a U.N. agency said.

Three air attacks targeted heavily crowded areas, including a mosque during prayer time on Saturday, in the town of al-Quriyah, UNICEF said in a statement.

Deir Ezzor city, the provincial capital, has been a hotbed of conflict since ISIS militants captured the northern suburbs in January. The city has been a critical junction for ISIS, with roads east and south toward Iraq and west to areas it controls in Homs province, including Palmyra.

It is also surrounded by some of ISIS' most valuable oilfields, which have been intensively targeted by both U.S. and Russian airpower in recent months.