US-backed fighters launched a new offensive on Saturday to oust the Islamic State group from swathes of Syria's eastern Deir Ezzor province, a top commander announced.

The Syrian Democratic Forces are already fighting for IS's de facto capital in Raqa, and they will now aim to clear the jihadists from territory east of the Euphrates River, said Ahmad Abu Khawlah in a statement.

Syrian regime forces are fighting a separate offensive to oust IS from the Deir Ezzor provincial capital.