BEIRUT (AP) — A new rebel group boasting some 1,000 fighters launched an operation Sunday to capture Syria’s largest city, Aleppo, while government troops using helicopter gunships and heavy artillery rolled back opposition gains in the capital Damascus.

The spread of fighting into a second major metropolis displayed the rebels’ growing confidence even though they still can’t hold ground against the government’s heavy weapons, pushing Syria’s civil war toward a new phase of destructive urban combat.