Fighting raging between rival Islamist rebel factions to control a key opposition stronghold near Damascus since late last month has killed more than 300 fighters, a monitor said on Sunday.
The Syrian Observatory for Human Rights said the clashes in Eastern Ghouta pitted the Saudi-backed Jaish al-Islam faction, which has been taking part in peace talks in Geneva, against the Faylaq al-Rahman and Jaish al-Fustat groups, both led by Al-Nusra Front, Syria's Al-Qaeda affiliate.
"More than 300 fighters have been killed as Islamist rebel factions battle for influence in the Eastern Ghouta," since April 28, Observatory head Rami Abdel Rahman said.
He said most of the rebels killed belonged to Jaish al-Islam or Al-Nusra.
Abdel Rahman said the clashes broke out after several attacks launched by Faylaq al-Rahman on positions held by Jaish al-Islam in Eastern Ghouta, a belt of countryside and small towns east of the capital that seen heavy fighting throughout Syria's five-year-old civil war.
Ten civilians have also been killed, he added, including a doctor and a child.
Most of the rebels killed since late last month in Eastern Ghouta clashes are believed to be from Jaish al-Islam or Al-Nusra.
The doctor, identified as Nabil al-Daas, was the only specialist gynaecologist still practising in Eastern Ghouta. His death was also reported by the Syrian Arab Red Crescent.
Residents and local officials have tried to mediate an end to the clashes and have staged protests urging the rival forces to stop the bloodletting to no avail, according to the Observatory.
Fighting has continued intermittently with both sides setting up roadblocks and building defences across Eastern Ghouta, said the Britain-based monitoring group which relies on a network of sources on the ground for its reports.
Jaish al-Islam is the dominant rebel group in Eastern Ghouta. One of its leaders -- Mohammed Alloush -- was named as the opposition's chief negotiator at peace talks in Geneva.
Syria's fractured armed opposition movement has been ravaged by infighting, particularly between jihadist groups and their rivals.
More than 270,000 people have been killed and millions more been driven from their homes since the conflict began with protests against President Bashar al-Assad in 2011.