Police say gunmen in the volatile southern Philippines opened fire on a packed minibus this week, killing four people and wounding another two.

The attackers began shooting as the vehicle approached Parang town on Jolo Island early Tuesday. The area is a stronghold of al-Qaida-linked Abu Sayyaf rebels notorious for bomb attacks and kidnappings that have terrorized the region for more than two decades.

Regional Police Director Mario Avenido said Thursday the driver, an army corporal, a 90-year-old woman and a 28-year-old civilian were killed in the attack.

A military report said this week that the militants have launched more attacks in the last four years despite U.S.-backed offensives because authorities failed to isolate them from supporters.