ZAMBOANGA, Philippines Abu Sayyaf guerrillas beheaded four hostages and killed another man in a fresh kidnap raid, delivering a chilling riposte to a massive military pursuit in the southern Philippines, authorities said Friday.

According to AFP, the Muslim rebels, already holding two American and 19 Filipino hostages, raided Lamitan town on the southern island of Basilan shortly before midnight Thursday and seized 31 Christian residents.

The captives included four children, provincial Police Chief Superintendent Akmadul Pangambayan said.

Clad in black hoods and armed with knives, assault rifles and grenade launchers, the militants hacked another resident and left him for dead, then burned down a school before fleeing, Pangambayan said.

The man died in hospital a few hours later, according to radio reports from Lamitan.

Hours after the abductions, the headless bodies of four of the new hostages were found a few kilometers from their village, Pangambayan said.

The military said 11 other hostages were recovered later, leaving the gunmen with 16 from their Lamitan raid.

The attack was the first major Abu Sayyaf response to a military campaign which began last month to deprive the self-proclaimed Islamic separatists of their support base.

Last week, the rebels threatened reprisals against Christians after the government detained about 100 suspected Abu Sayyaf sympathizers.

Pangambayan said police and the military were pursuing the raiders, vowing "we will not let this thing pass".

But the abductions exposed the government to further embarrassment, with the military waging what has so far been a fruitless campaign to free hostages including three Americans seized from a tourist resort in May.

One of the Americans, Peruvian-born Californian Guillermo Sobero, is presumed dead.

One of the 11 who escaped from the Lamitan raid, 17 year-old student Ian Rebollos, recounted how he fought back and wrested a kidnapper's rifle away as he was about to be hacked with a machete.

"They just barged into our houses and grabbed us at gunpoint," Rebollos told radio Mindanao network.

He said the kidnappers told him they were followers of "commander robot", the pseudonym of Ghalib Andang, a leader of the Abu Sayyaf in the nearby island of Jolo.

The Abu Sayyaf rebels have taken further hostages since the May raids as they elude 5,000 pursuing troops in the Basilan jungles.

While they have freed some Filipinos, reportedly in exchange for hefty ransoms, the Abu Sayyaf have also killed four Filipino hostages and claim to have beheaded Sobero.

The other Americans are Christian missionary couple Martin and Gracia Burnham, both Kansas natives.

The rebels are believed to have taken their latest hostages toward the Muslim-dominated town of Tuburan, a known stronghold of the kidnapping gang.

The Abu Sayyaf have been kidnapping Christians and foreigners in the impoverished south for years, demanding large ransom payments and sometimes killing their captives.

They insist they are Islamic independence fighters but the government considers them mere bandits.

Meanwhile, the Philippines' two largest Muslim separatist factions agreed Friday to unite to forge a lasting peace in the impoverished southern Philippines.

According to an AFP report, the deal between the Moro National Liberation Front (MNLF) and the Moro Islamic Liberation Front (MILF) was reached after two days of intensive talks in Cyberjaya, about 50 kilometers (31 miles) south of Kuala Lumpur.

The MNLF has already struck a peace deal with the Philippine government, while the MILF is holding talks with manila in Malaysia for a separate peace agreement.

Malaysian Defense Minister Najib Razak witnessed the "initializing" of the agreement -- marking an intent to unite -- with the actual signing to take place when Philippine President Gloria Arroyo makes a two-day visit here from Tuesday.

Najib said the breakup of the MNLF, which led to the formation of the MILF in 1976, had been a setback to the Muslim struggle in the largely Roman Catholic Philippines.

"The consequences of this breakup had far-reaching effects on the leadership of the Moro (Philippine Muslim) people and fragmented the directions of your struggle," he said at the ceremony.

"The agreement will provide (a) new platform for a more lasting solution to resolve the Moro people's problem," the Malaysian minister said.

The accord will give the two factions a united front in cooperating with the Philippine government, Najib noted.

MNLF Vice President Hatimil Hassan said unity was crucial to promoting peace and prosperity in the poverty-struck southern Philippines. The group would not push for an Islamic state but greater autonomy, he added.

"There are Muslims and Christians there. We respect all religions. We will not push for an Islamic state but we will leave that to the people," he told AFP.

The MILF's Vice Chairman for Military Affairs, Murad Ebrahim, said the unity agreement would promote the peace cause after three decades of insurgency.

"We should leave behind the differences that set us apart and together as one, let us move forward and secure for ourselves the bounties of freedom which have been denied the moro people for so long," he said.