Islamic State group militants have "executed" eight Syria soldiers following an ambush, a war monitor said Sunday, reporting 14 troops killed by the jihadists in recent days.

IS overran large swathes of Syria and Iraq in 2014, proclaiming its "caliphate" and launching a reign of terror.

It was defeated territorially in Syria in 2019, but its remnants continue to carry out deadly attacks, particularly in the vast Badia desert which runs from the outskirts of Damascus to the Iraqi border, mainly targeting pro-government forces and Kurdish-led fighters.

IS cells "executed eight members of the regime forces... including an officer" following the ambush this week in the desert in eastern Syria, the Syrian Observatory for Human Rights monitor said Sunday.

The troops were heading from Sukhna towards the city of Deir Ezzor when they were attacked, the Observatory said, without specifying when exactly they were killed.

IS jihadists also killed six other soldiers this week "after they were taken prisoner" following a separate ambush along the road between Sukhna and Palmyra in Homs province, said the Britain-based Observatory, which relies on a network of sources inside Syria.

Since the start of the year, more than 200 soldiers and affiliated fighters have been killed in IS attacks, ambushes and explosions in the Syrian desert including in Deir Ezzor, Homs and Raqa provinces, the Observatory said.

Jihadist attacks have killed at least 37 civilians during the same period, while government forces and affiliated fighters have killed 24 IS members, according to the Observatory.

Last week, the monitor said an IS attack in northern Syria killed at least 11 people who were searching for desert truffles, a delicacy which fetches a high price in the war-torn country.

Between February and April each year, hundreds of impoverished Syrians risk their lives to forage for truffles in the Syrian desert, which in addition to being a jihadist hideout is also littered with mines.

A United Nations report released in January said IS's "combined strength" in Iraq and Syria "was assessed at between 3,000 and 5,000 fighters". 

In Syria, IS "has intensified attacks since November", the report said, adding that the central Badia desert "served as a logistics and operations hub" for the group.

The Observatory said that with its recent escalation, IS is seeking "to show it is able to launch attacks despite having lost" its territorial control five years ago.