Beirut (AFP) - Syrian government troops advanced 13 kilometres (eight miles) on Sunday in the eastern province of Deir Ezzor as they pressed an offensive against the Islamic State group, a monitor said.

The Britain-based Syrian Observatory for Human Rights said troops of the Damascus regime pushed into the southwest of the oil-rich province from the desert town of Sukhnah.

In June, Syrian troops broke into Deir Ezzor from a border region with Iraq and earlier this month they breached it from the neighbouring province of Raqa, but moving just four kilometres in.

Observatory chief Rami Abdel Rahman said Sunday's advance was the first carried out from the Badia desert region.

Since May, Syria's army has been conducting a broad military campaign with Russian support to recapture the Badia that separates the capital Damascus from Deir Ezzor.

Most of Deir Ezzor has been held by IS since 2014, and jihadists have also besieged government forces and civilians inside the provincial capital Deir Ezzor city since 2015.

On Thursday, regime forces backed by Russian warplanes completely surrounded the jihadists in a vast central desert region.

Fierce clashes erupted in that area on Sunday, the Observatory said, adding that the region was also struck by more than 50 air strikes overnight.