Damascus, Sep 11 (IANS): The Syrian army on Sunday captured the Tharda Mountains in the southern rim of Deir al-Zour province in eastern Syria, securing the airbase of Deir al-Zour, a military source said.

The capture of the Tharda Mountains has secured the vicinity of the airbase of Deir al-Zour, as the mountains function as the airbase's first defence line, Xinhua cited the military source as saying.

A day earlier, the Syrian army and allied troops broke the Islamic State (IS) siege on the airbase, just a week after lifting the IS' three-year siege on the capital city of Deir al-Zour.

Speaking on condition of anonymity, the source said that the US had bombed Syrian army in the Tharda Mountains in September 2016, during which 90 soldiers were killed.

The US strike facilitated the IS control over the mountains in 2016.

The terrorists had suffered big losses due to the advance of the Syrian forces in Tharda Mountains, the source said, adding that many IS commanders had fled to the city of Bukamal in the countryside of Deir al-Zour.

The source said that to capture the mountains, Syrian forces had launched offensives from two directions; one from the Panorama roundabout at the southern entrance of Deir al-Zour capital city, the other one from the Tyem energy field in the southern countryside of Deir al-Zour province.

The progress comes as Syrian army on Sunday seized full control of the main road from the capital Damascus to Deir al-Zour city in eastern Syria, stripping the IS of key areas along the road.