MANILA, Philippines -- Hundreds of troops, backed by assault helicopters, launched offensives on two strongholds of a breakaway Muslim guerrilla group in southern Philippines after they attacked at least 14 military camps and outposts, officials said Thursday.

The brazen attacks since Sunday left at least four soldiers dead including one who was beheaded, while at least two rebels were killed in the counteroffensive, according to the government. But a regional army spokesman, Col. Prudencio Asto, said the rebel death toll had reached 15 by Thursday, citing intelligence reports. This could not be independently confirmed.

The rebel group broke off last year from the larger Moro Islamic Liberation Front, which is involved in peace talks with the government. Known as the Bangsamoro Islamic Freedom Movement, it opposes the negotiations, and has vowed to continue fighting for an independent homeland for minority Muslims in the south of the predominantly Roman Catholic nation.

The group's leader Ameril Umbra Kato had a stroke in November, plunging his group into uncertainty, but the renewed fighting indicates he still has firepower.

Governor Mujiv Hataman said the military and police have strengthened security in public areas in a five-province Muslim region that he heads to prevent diversionary attacks like bombings from Kato's fighters.

"We cannot allow any group to carry out brazen attacks and get away with it," Hataman said.

Troops were moving cautiously to avoid widespread disruptions amid the Muslim fasting month of Ramadan, he said. More than 25,000 residents have been displaced by the fighting, according to the Office of Civil Defence.

The fighting this week is among the worst since 2008, when the peace talks bogged down, igniting clashes between Moro Islamic Liberation Front forces and government troops in Maguindanao and outlying provinces. That fighting killed hundreds and displaced 750,000 people before the two sides agreed to a cease-fire.

The government says the attacks by Kato's forces on 14 military camps, detachments and outposts were meant to derail its negotiations with MILF, which are being brokered by Malaysia. Still, the talks resumed in Malaysia Wednesday.

Military officials said army assaults were focused on a vast marshland and two abandoned villages in Maguindanao's Datu Unsay town where the breakaway rebels have taken position. Army troops, backed by artillery and tank fire, have advanced slowly in areas rigged with booby traps.

A key Maguindanao highway which was closed down after rebel sniper fire killed two passing commuters earlier in the week was briefly reopened and then shut again Thursday due to lingering threats, regional deputy military commander Romeo Santiago Nebres said.