Russian air strikes on Sunday morning killed at least 53 civilians, including 21 children, in a village held by the Islamic State group in Syria's eastern Deir Ezzor province, a monitor said in a new toll.

"The toll increased after removing the debris in a long day of rescue operation," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights told AFP, adding the strikes hit "residential buildings" in the village of Al-Shafah on the Eastern bank of the Euphrates River.

The monitor previously gave a toll of 34.