Syrian rebels turned the gun of a captured tank against government forces on Thursday, shelling a military airbase expected to be used as a staging post for army reinforcements in the battle for Aleppo.President Bashar al-Assad’s troops meanwhile bombarded the strategic Salaheddine district in Aleppo itself with tank and artillery fire while rebels tried to consolidate their hold on areas they have seized.In the capital Damascus, troops overran a suburb on Wednesday and killed at least 35 people, mostly unarmed civilians, residents and activist organisations said.The fighting for Syria’s two biggest cities highlights the country’s rapid slide into full-scale civil war 17 months on from the peaceful street protests that marked the start of the anti-Assad uprising.World powers have watched with mounting concern as diplomatic efforts to find a negotiated solution have faltered and violence that has already claimed an estimated 18,000 lives worsens.More than 180 people were killed in Syria on Wednesday, 133 of them civilians and 45 of them members of Assad’s forces, according to the opposition Syrian Observatory for Human Rights.The rebels’ morale was boosted when they turned a government tank’s gun on the Menakh airbase 35 km (25 miles) north of Aleppo - a possible staging post for army reinforcements."We hit the airport using a tank that we captured from the Assad army. We attacked the airport a few times but we have decided to retreat at this time,” a rebel fighter named Abu Ali told Reuters. The pro-opposition Observatory said government forces at the airbase had used artillery and rocket launchers to bombard the town of Tel Rifaat, which lies between the airbase and Aleppo, Syria’s commercial centre.Reuters correspondents heard heavy weapons fire on Thursday morning from Salaheddine in southwest Aleppo, a gateway to the city of 2.5 million people that has been fought over for the past week.