Syria's army and allied fighters have captured the city of Deir Ezzor from the Islamic State group in a Russian-backed operation, a monitor said on Thursday.

There was no immediate confirmation from official sources, though state media earlier reported army advances in the city in the country's east.

"Regime forces and allied fighters... with Russian air support have full control of Deir Ezzor city," the Britain-based Syrian Observatory for Human Rights said.

"Fighting has ended, now there are sweeping operations under way," Observatory director Rami Abdel Rahman said.

Earlier, the Observatory and Syrian state media reported Syrian government troops had captured three new neighbourhoods from the jihadists.

But a military source had said the government only held around 80 percent of the city.

Syria's army broke into Deir Ezzor in September, ending an IS siege of nearly three years on government-held parts of the city.

IS once held most of Deir Ezzor province, an oil-rich region that runs along the eastern border with Iraq.

But it is under attack from two separate campaigns, including the regime's Russian-backed assault, and another operation by the US-backed Syrian Democratic Forces, an alliance of Kurdish and Arab fighters.

source: AFP