Opposition forces seeking to overthrow Syria's President Bashar al-Assad launched their biggest offensive in years last week, retaking the northern city of Aleppo and driving government forces out of the region.

Airstrikes also hit residential buildings in the city of Idlib, which has become a refuge for people displaced by the civil war, killing at least 12 civilians, according to the White Helmets, an independent rescue organization.

Rebels captured Syria's second-largest city, Aleppo, over the weekend and advanced toward Hama in a surprise incursion that reignited Syria's 13-year-old civil war and embarrassed President Bashar al-Assad's forces.