The rebels have cut off the highway, which the army has been using to transport troops and supplies to a military base within the airport complex. Rebels have made other advances in the battle for the airport in recent weeks, including overrunning two army bases along the road to the airport.
The rebels also control large swaths of countryside outside Aleppo and whole neighborhoods inside the city, which is carved up into areas controlled by the regime and others held by rebels. Months of heavy street fighting has left whole neighborhoods of the storied city in ruins.
On Friday, regime forces fired three missiles into a rebel-held area in eastern Aleppo, hitting several buildings and killing 37 people, according to the Observatory. Some bodies were recovered from the rubble of apartments flattened in the strike, which apparently involved ground-to-ground missiles.
A similar attack on Tuesday in another impoverished Aleppo neighborhood killed at least 33 people, almost half of them children.
In Damascus, government forces shelled several rebellious suburbs Saturday as part of their efforts to dislodge opposition fighters who have used the towns and villages surrounding the capital as a staging ground for their attempts to push into the center of the city.
Recent rebel advances in the suburbs, combined with the bombings and three straight days of mortar attacks earlier this week, marked the most sustained challenge to the heart of Damascus, the seat of Assad's power.
A suicide car bombing on Thursday near the ruling Baath Party headquarters in central Damascus killed 53 people and wounded more than 200, according to state media. Anti-regime activists put the death toll at 61, which would make it the deadliest bombing of the revolt in the capital.
The different tolls could not be reconciled.
Nobody has claimed responsibility for the attack. Car bombs and suicide attacks have been a hallmark of Jabhat al-Nusra, an Islamic militant group that is one of the myriad factions fighting on the rebel side. Nusra fighters, the most effective group on the battlefield, have led assaults on military installations and control swaths of territory in the north, including parts of Aleppo.
The fighting has increasingly taken on sectarian overtones with members of Syria's Sunni Muslim majority dominating the rebel ranks, who are fighting Assad's regime that is mostly made up of Alawites, an offshoot Shiite group.