The rebels are outgunned by regime forces, which have gained momentum since President Bashar Assad agreed to relinquish his chemical weapons stocks, averting the threat of imminent U.S. military action. But they often are able to engage in deadly battles.
Syria's civil war has cleaved along the country's sectarian patchwork. Majority Sunni Muslims dominate the revolt, which began in March 2011, while Christians and other Muslim sects have mostly stood behind the regime.
But the opposition itself faces growing divisions and internal fighting as the Western-backed rebels blame al-Qaida linked extremists for tarnishing their image and preventing the U.S. and its allies from providing crucial support.
On Saturday, al-Qaida fighters of the Islamic State in Iraq and the Levant and Jabhat al-Nusra clashed with Kurdish gunmen clashes in the northeastern province of Hassakeh, the Observatory said. It had no immediate word on casualties.
Gen. Salim Idris, the commander of the Western-backed Free Syrian Army and the Supreme Military Council, met with senior officers from the political Syrian National Coalition on Saturday to call on all factions to close ranks and renounce divisions.
The statement emphasized the need "to expedite the process of unification of all groups of the military wing through the restructuring of the FSA" and called the SNC the "political umbrella of revolutionary action."
It also rejected "any dialogue" with the regime, saying it will only enter negotiations that lead to Assad's resignation.
The meeting came days after 43 rebel brigades around Damascus announced that they were banding together to form a breakaway group called the Jaish al-Islam or Army of Islam under the leadership of the head of one of the most powerful factions, Liwa al-Islam another blow to the mainstream political opposition, which is dominated by exiles and accused of not being in touch with events on the ground.
A U.N. resolution has endorsed a roadmap for a political transition in Syria adopted by key nations in June 2012, and called for an international conference to be convened "as soon as possible" to implement it.
But Syrian Foreign Minister Walid al-Moallem put a damper on those efforts, saying senior Damascus government officials would not sit down to talk with the coalition because it had supported the possibility of a U.S. strike.
The conflict has shattered Syria's economy, killed more than 100,000 people and forced over 2 million from their homes.
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Follow Bassem Mroue on twitter.com/bmroue