The Syrian government said it has recaptured a district of Aleppo, but rebels have vowed to fight on. Rebels have lost a third of their sector of the city in recent days, bringing them to the brink of a catastrophic defeat. Gains by the Syrian army and its allies have brought whole districts back under government control. Their moves have also led to thousands fleeing destroyed neighborhoods. A rebel official said government forces have stepped up the use of air strikes.