Syrian rebels attack air base to secure north-south corridor BEIRUT (Reuters) - Syrian rebels attacked a military airport in the country's north on Saturday in a push to cut off Syria's biggest city Aleppo from the capital Damascus, and secure a strategic north-south corridor. President Bashar al-Assad's forces appear over-stretched with fewer fighters on the ground and have sought to limit rebel advances with far superior firepower, increasingly from the air and especially in the Aleppo and Damascus areas. But despite ragged command-and-control and few heavy weapons, the rebels have gained control over the rural north and border crossings to Turkey after 19 months of conflict and now seek to isolate Aleppo from Assad's power fulcrum in Damascus. Abroad, fragmented anti-Assad opposition groups will try again at a meeting in Qatar starting on Sunday to form a united front in pursuit of international respect and, most important, better weapons to turn the battlefield tables and oust Assad. Fighters from the Islamist Front to Liberate Syria said they launched the attack on the Taftanaz military airport in the northern province of Idlib in the early hours on Saturday, using rocket launchers and at least three tanks. The government has used Taftanaz to fuel helicopter gunships and fighter jets that have bombarded nearby villages. "All planes that bomb Idlib take off from that airport, and also, if we liberate it, the road between Aleppo and Idlib will be open and safe," a rebel from the Sukour al-Sham brigade said. "We have managed to destroy one helicopter and several anti-aircraft batteries, and we are using tanks to shell the base," he told Reuters by phone from the scene. Syrian warplanes attacked the nearby village of Bennish in retaliation, the Britain-based Syrian Observatory for Human Rights said. Further fighting was reported in the eastern, oil-producing province of Deir al-Zor and on the outskirts of Damascus. The revolt against Assad began as peaceful rallies calling for more freedoms and democracy but turned to armed struggle against the military machine that he unleashed on protesters. Diplomatic intervention has been fruitless because major world and regional powers are at loggerheads over how to end the conflict. It has killed about 32,000 people, making it the bloodiest of Arab uprisings that have ousted entrenched leaders in Tunisia, Egypt, Libya and Yemen since early last year. On Friday government troops vacated their last base near the Saraqeb, leaving Idlib town and its surroundings "completely outside the control of regime forces," the Observatory said. The pullout followed coordinated rebel attacks on Thursday on three military posts around Saraqeb, 50 km (30 miles) southwest of Aleppo, in which 28 soldiers were killed. Saraqeb lies at the confluence of Syria's main north-south highway, linking Aleppo with Damascus, and another road connecting Aleppo to the Mediterranean port of Latakia, a stronghold of Assad's minority Alawite community. Shi'ite Iran remains the staunchest regional supporter of Assad, whose Alawite faith derives from Shi'ite Islam. The conflict has been increasingly seared by sectarian bloodshed U.N. rights officials say may amount to war crimes. The rebels suffered a setback in image this week when the United Nations said a video released on Wednesday appeared to show them executing soldiers who had surrendered after the insurgents occupied the base near Saraqeb. A video posted on Saturday on YouTube by anti-Assad activists appeared to show government forces mutilating bodies of rebels in one area of Idlib. In two sequences, soldiers cut off ears of dead rebels while cursing them. "This is the ear of a dog," a voice behind the camera says with a laugh. In response to rebel territorial gains, Assad has cranked up air strikes on opposition strongholds, including working class suburbs east of Damascus over the last week. The bloodshed has endured despite an attempted ceasefire, proposed by join U.N.-Arab League envoy Lakhdar Brahimi to mark last month's Muslim holiday of Eid al-Adha. Political divisions within the opposition, a lack of cohesion between their leaders abroad and fighters in Syria, as well as the rising profile of Islamist militants in rebel ranks, have put off Western states otherwise keen to see Assad fall. On Wednesday, the United States called for an overhaul of the Syrian opposition leadership, saying it was high time to move beyond the feud-ridden Syrian National Council (SNC) and bring in those "in the front lines fighting and dying." Secretary of State Hillary Clinton, signaling a more active approach by Washington to fostering a credible opposition to Assad, said the meeting in Qatar would be an opportunity to broaden the coalition against him. Veteran opposition leader Riad Seif has proposed a structure melding the rebel Free Syrian Army, regional military councils and other insurgent units alongside local civilian bodies and prominent opposition figures. Called the Syrian National Initiative, his plan envisages the creation of an Initiative Body, including political groups, local councils, national figures and rebel forces; a Supreme Military Council; a Judicial Committee and a transitional government-in-waiting composed of technocrats. Writing by Mark Heinrich; Editing by Louise Ireland