Gunmen killed at least 15 people in Syria, mostly army soldiers travelling on a bus, in the second such road ambush in recent days, a war monitor said Monday.

The attack late Sunday resulted in the deaths of eight soldiers, four allied fighters and three civilians, the Britain-based Syrian Observatory for Human Rights said, updating an earlier toll.

There was no immediate claim of responsibility, but the monitor said the Daesh terror group was to blame.

Another 15 people were wounded, with cars and fuel tankers also attacked, in the Wadi Al Azib area of Hama province.

Syria's official news agency SANA said the "terrorist attack" killed nine people, all civilians.

Last week, Daesh said it had ambushed a bus on December 30 in Syria's eastern Deir Ezzor province, killing at least 37 soldiers.

Daesh in 2014 overran large parts of Syria and Iraq and proclaimed a cross-border "caliphate" before multiple offensives in the two countries led to its territorial defeat.

The group was overcome in Syria in March 2019, but sleeper cells continue to launch attacks in the vast Badia desert, which runs from central Syria eastwards to the border with Iraq.

"The group has since last spring been ramping up its activities and launching attacks against government  forces in the Badia," Observatory chief Rami Abdel Rahman said.

Analyst Aymen Al Tamimi said the latest ambushes reflected the difficulty in stamping out sleeper cells in such a broad region.

"The Syrian government forces and its allies have to cover a very large, sparsely populated area that is easy for Daesh to survive in and conduct attacks," he said.

More than 387,000 people have been killed and millions forced from their homes since Syria's civil war broke out in 2011.