MANILA (Updated, 11:26 a.m.) -- Communist rebels opened fire on two army vehicles in the remote southern Philippines, killing four troops, an official said Thursday.

A civilian caught in the crossfire was among four wounded in the ambush Wednesday in Agusan del Sur province, where the rebel New People's Army has stepped up raids on police outposts and military convoys, said army spokesman Maj. Randolph Cabangbang.

The rebels, believed to be numbering about 5,000 fighters, have waged a 41-year rural-based insurgency that has led to human rights abuses and has stunted economic development.

President Gloria Macapagal Arroyo has ordered the military to defeat the rebels by the end of her term in June, but they have dismissed the deadline as illusionary and part of psychological warfare.

Troops had just held a meeting with residents of Masayan village and were heading to another village to prepare for a medical mission when they were ambushed, Cabangbang said. The rebels withdrew after the gunfight, he said.

Peace talks between the rebels and the government, brokered by Norway, collapsed in 2004 after the guerrillas blamed the Philippine government for their inclusion on U.S. and European lists of terrorist groups. (AP)