Syria's army has ambushed opposition fighters in the Qalamoun Mountains, north of the capital Damascus, leaving dozens dead, the Syrian Observatory for Human Rights and state media reported.
Friday’s attack happened between the Christian town of Maaloula and the town of Yabroud, where government forces and rebels are fighting.
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The UK-based Observatory said as many as 60 people were killed in the attack.
Syrian state television showed footage of dozens of bodies lying in a mountainous area, with machine guns and rocket-propelled grenades next to them.
"There were about 400 of us including Saudis, Chechens and other nationalities," a badly wounded fighter who was lying on the ground told a state television reporter who was asking him about numbers and nationalities.
The fighter said he belonged to Liwaa al-Islam, a self-declared jihadist group that is one of the biggest rebel units fighting to topple the regime of President Bashar al-Assad.
The state television reporter said the army tracked the fighters overnight and ambushed them on their way to the town of Jayrud, 20km southeast of Yabroud.
It was not possible to verify the report independently due to restrictions on the media in Syria.
In the town of Yabroud, on the Damascus-Homs highway, several casualties were reported amid intense shelling by regime troops.
Syria's almost three-year-long conflict between forces loyal to Assad and mostly Sunni Muslim rebels has killed more than 120,000 people since March 2011.