Helicopters pounded areas controlled by the Moro Islamic Liberation Front (MILF) near the town of Mamasapano on Mindanao island after the rebels attacked an army outpost in violation of a two-year-old ceasefire. 

Colonel Franklin del Prado, spokesperson of the Philippine army's 6th Infantry Division in the area, said on Monday the slain soldiers all belonged to the battalion base attacked by the MILF. 

He said reports from the field indicated that at least 13 MILF rebels died in the counter-offensive.