At least 21 combatants died Monday in clashes between renegade Muslim rebels and government troops in the southern Philippines, but an 18-month-old cease-fire remains intact, officials said. Malaysia, Brunei and Libya have some 60 cease-fire monitors in the southern Philippines who, together with government and rebel Moro Islamic Liberation Front representatives, were trying to reach the scene of the fighting, rebels' spokesman Eid Kabalu said. The clashes erupted when 60 to 100 MILF guerrillas attacked an army detachment in Mamasapano, a town in Maguindanao province about 900 kilometers (550 miles) south of Manila, military spokesman Lt. Col. Buenaventura Pascual said. Kabalu said the attack came in retaliation for the killing by the military of a local MILF commander, Abdul Rahman Bides Binago. But the attack was not sanctioned by the MILF leadership, he said.