Taliban gunmen stormed a Pakistani Air Force base early on Friday, killing at least 20 people, the deadliest attack on a military installation this year.

Sixteen of the dead were killed in a mosque as they offered morning prayers, and a captain died leading the counterattack against the raiders, 13 of whom were killed, military spokesman Major General Asim Bajwa said on Twitter. Three air force guards also were killed.

It was unclear if the 16 killed in the mosque at the Badaber air base in the northwestern city of Peshawar were civilians or military.