BEIRUT – A rebel unit of army defectors launched a major offensive against security facilities in Syria’s largest city of Aleppo, and anti-regime forces targeted air bases to try to reduce the military threat from the skies, activists said Friday.

The attacks by the Brigade of Free Syrians pointed to a higher degree of planning by the rebels, suggesting that President Bashar Assad’s opponents are becoming more brazen.

The Local Coordination Committees, an activist group that monitors violence and rights abuses in Syria, said rebels shot down a helicopter in the town of Sarmeen. An activist in the area also reported a helicopter was downed.