Separate Russian and US-led coalition air strikes on Tuesday killed 28 civilians in Syria's eastern Deir Ezzor province, where rival offensives against the Islamic State group are under way, a monitor said.

The province lies along Syria's border with Iraq and is seen as a strategic prize by both Russian-backed Syrian troops and an alliance of Arab and Kurdish forces supported by the US-led air coalition.

On Tuesday, deadly coalition raids struck the village of Al-Shahabat, according to the Britain-based Syrian Observatory for Human Rights.

"Coalition air strikes killed 12 members of a single family, among them five children, in a village on the eastern banks of the Euphrates River," said Observatory head Rami Abdel Rahman.

He said fierce fighting between jihadists and the US-backed Syrian Democratic Forces was raging around IS-held Al-Shahabat, which lies around seven kilometres (four miles) away from the river.

The Euphrates slices across Deir Ezzor province diagonally.

Syrian government troops are fighting across the river on its western side as part of a separate assault that is backed by Moscow.

Russian air strikes on Tuesday hit a cluster of tents on the western banks of the Euphrates, killing "16 civilians including five children," according to Abdel Rahman. 

He said civilians had set up the tents on the edge of the Zaghir Shamiyah village after fleeing their homes fearing clashes.

The strikes follow three days of deadly suspected Russian raids in Deir Ezzor province that have killed dozens of civilians, according to the Observatory.