At least 15 people in Syria, mostly government soldiers, were killed in an ambush on a bus on the main highway in the central Syrian desert, an attack that is by suspected Islamic State militants, a war monitor said Monday.

The ambush on late Sunday, the second such road incidents in less than a week, 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 Islamic State 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, the IS group said it ambushed a bus on December 30 in Syria’s eastern Deir Ezzor province, killing at least 37 soldiers, including 8 officers, and 12 others wounded. Sone of those injured were in critical condition.

The extremist group overran large parts of Syria and Iraq and proclaimed a cross-border “caliphate” there in 2014, 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. After losing key areas across Syria, the IS militants moved to the desert areas in eastern Syria, where they frequently carry out attacks on military personnel and bases.

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