BEIRUT (AP) — Syrian activist groups say rebels have captured a major air base in the north of the country after months of fighting.

The Aleppo Media Center says rebels took Mannagh helicopter base before dawn Tuesday. The Britain-based Syrian Observatory for Human Rights says the base fell nearly 24 hours after rebels launched an all-out offensive against it.

Rebels have been trying since last year to capture Mannagh, which is near the Turkish border in Aleppo province, but faced strong resistance from troops defending it.

The capture of the base is a blow to President Bashar Assad's forces because it deprives them of one of their main outposts in the contested province.

The Observatory said there were casualties on both sides. It added that rebels took prisoner a number of government troops.