FILE PHOTO: Syrian Democratic Forces (SDF) stand on their military vehicle in northern Deir al-Zor province ahead of an offensive against Islamic State militants, Syria February 21, 2017. REUTERS/Rodi Said

BEIRUT (Reuters) - The Syrian army and its allies advanced in the central Syrian desert on Monday and could soon encircle an Islamic State pocket, part of a multi-pronged thrust into eastern areas held by the jihadist group.

A Syrian military source said the Syrian army and its allies had taken a number of villages around the town of al-Koum in northeastern Homs province.

This leaves a gap held by Islamic State of around only 25 km (15 miles) between al-Koum and the town of al-Sukhna to its south, which was taken by the Syrian government on Saturday.

If the army, supported by Russian air power and Iran-backed militias, closes this gap they will encircle Islamic State fighters to their west in an area of land around 8,000 km square, the Syrian Observatory for Human Rights said.

The Russian Defence Ministry said on Monday that it had contributed to this advance by advising on an airborne landing of pro-government troops north of al-Koum on Saturday.

The operation allowed them to take the al-Qadeer area from Islamic State militants before proceeding to al-Koum, Russia’s TASS news agency reported.

Islamic State has lost swathes of Syrian territory to separate campaigns being waged by Syrian government forces backed by Russia and Iran, and by the U.S.-backed Syrian Democratic (SDF) Forces, which is dominated by the Kurdish YPG militia. The SDF is currently focused on capturing Raqqa city from Islamic State.

Syrian government forces advancing from the west have recently crossed into Deir al-Zor province from southern areas of Raqqa province.

Islamic State controls nearly all of Deir al-Zor province, which is bordered to the east by Iraq. The Syrian government still controls a pocket of territory in Deir al-Zor city, and a nearby military base.