BEIRUT – Syrian rebels knocked down army defenses and moved in on the country's second largest airport Wednesday, reportedly killing more than 40 soldiers and bringing them closer to what could be their biggest conquest since the beginning of the civil war.

Control of Aleppo international airport and a military air base next to it would be a huge strategic shift for Syria's northeastern region, giving the opposition a potential air hub enabling aid and other flights.

Still, activists said it could be days before the rebels would be able to push their way into the airport, 4 miles from the contested city center, and even then, it was unclear whether they would be able to retain control of the sprawling facility for long.