Syrian regime forces were locked in fierce clashes with "Islamic State" (ISIS) terrorists  on Tuesday on the outskirts of a key town near the ancient city of Palmyra, a monitor said, according to AFP.

Just two days after seizing Palmyra from ISIS, pro-government fighters advanced southwest towards the jihadist-held town of Al-Qaryatain. They seized a series of hilltops overlooking the town during the night and battled ISIS terrorists into the afternoon, according to the Syrian Observatory for Human Rights.

The Britain-based monitor said the troops were backed by both Syrian and Russian air raids.