A senior Hezbollah commander has reportedly been killed battling Syrian rebels in the Qalamoun mountains on the border with Lebanon.
Syrian opposition-affiliated sources are claiming Marwan Mughniyeh was killed along with seven other Hezbollah terrorists during fierce fighting with the Army of Conquest - a rebel alliance led in great part by Al Qaeda's Nusra Front.
He was a cousin of Jihad Mughniyeh - himself a senior Hezbollah commanders killed in an Israeli airstrike in January - and Jihad's father Imad Mughniyeh, the Hezbollah terrorist mastermind killed in 2008 in what is also suspected to have been an Israeli assassination.
Marwan Mughniyeh was one of scores of casualties on both sides in a pro-Assad regime offensive to wrest control over the remainder of the strategically-important Qalamoun area from rebels.
Hezbollah announced on its Al-Manar television channel that it and Syrian regime forces had taken Al Nusra Front's largest base in the region, at Sahlet al-Maaysra.
On Tuesday, Hezbollah chief Hassan Nasrallah threatened to expel the insurgents from the area. Since then, the Iranian-sponsored terrorist group has taken several positions with regime air support, according to the Observatory and Syrian military sources.
The Qalamoun region straddles the Syria-Lebanon border and was a rebel stronghold until a major operation last year by Syrian regime troops backed by Hezbollah.
But rebels still retain a foothold in the region, which is a key supply line for weapons, supplies and fighters from their supporters in Lebanon.
AFP contributed to this report.