Syrian rebels fought pitched battles against government forces at a military base protecting the civilian airport in Aleppo today.
Rebels have been attacking the civilian airport for weeks and now claim to have over-run the main defences of the facility.
However the airport itself, which stopped handling any flights weeks ago because of the fighting, still remains in government hands.
Opposition fighters captured large parts of the Brigade 80 base near the airport on Tuesday and attacked another major air base, Nairab, adjacent to it after taking control of al-Manara army checkpoint outside it.
The rebels claimed that they were "almost fully in control" of the "Brigade 80" base.
A rebel spokesman claimed that more than 40 government troops had been killed in the fighting, including two brigadier generals, a colonel and two lieutenant colonels.
But heavy fighting was still raging for control of the Nairab base as well as the airport itself, which both have their own defences in addition to the protection provided by Brigade 80.
Syria's rebels have claimed several strategic victories in recent days, boasting of capturing a military air base in the province of Aleppo on Tuesday and the country's largest dam on the Euphrates River the day before.
But there were heavy clashes outside Damascus today, with government warplanes hitting several suburbs to dislodge opposition fighters from around the capital.
Fighter jets also carried out air strikes on rebel positions in the province of Homs.
The rebels had been pushing their way into Damascus since last week and came to within a mile of the heart of the capital last Friday.
However the government has clamped down in Damascus, setting up checkpoints and controlling movement in and out of the city with some of the government's most loyal troops.
UN human rights chief Navi Pillay warned on Monday that the number of people killed in Syria is probably now approaching 70,000.
She told the UN security council that there have probably been almost 10,000 new deaths in recent weeks, adding that the council's deep division over the conflict had been "disastrous."
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