The Syrian branch of Al Qaeda - Jabhat al-Nusra (the Nusra Front) - has released video it says are of clashes between its men and Hezbollah fighters loyal to Syrian president Bashar al-Assad.
The footage appears to be from the mountainous Qalamoun region on the border with Lebanon.
The Syrian Observatory for Human Rights said that seven Hezbollah fighters were killed in fighting with Sunni Islamist rebels on Monday, and 31 more were wounded. 16 rebels were also killed, although the Nusra Front claims to have successfully captured positions from pro-Assad forces.
It comes as the Nusra Front and other rebel groups are losing ground to the radical "Islamic State" or ISIS, which broke away from Al Qaeda last year and recently declared an Islamic "Caliphate" in parts of Syria and Iraq it controls.
Hezbollah has absorbed serious casualties since enlisting to help its allies in Damascus, with a steady flow of fighters returning dead or wounded to Lebanon.