The Philippine army on Thursday sent hundreds of extra troops to contain a powerful Muslim clan whose members have been indicted for the political massacre of 57 people.

The extra battalion of 400 soldiers brings to more than 3,000 the number now guarding the home of the Ampatuan clan and government offices in Maguindanao province, military spokesman Lieutenant Colonel Romeo Brawner said.

"Our forces are now stationed in the area. They are restricting their movement within the compound (home)," Brawner told AFP.

Supporters of the clan, which has ruled strife-torn Maguindanao for a decade and has its own private army, were being barred from entering the home in the provincial capital of Sharrif Aguak, Brawner said.

The move is also meant to support the national police if arrest warrants are issued for several clan members who could be charged with murder, including the patriarch Andal Ampatuan Snr, he said.

"Right now the security is very tight in the area. We are stopping their supporters from entering their home," Brawner said.

Brawner said about 10 armoured personnel carriers and tanks had also been deployed to Maguindanao.

The clan patriarch's son and namesake, Andal Ampatuan Jnr, was arrested three days after the November 23 massacre and has been charged with 25 counts of murder so far. Authorities said he will likely face more charges.

Police have also indicted Ampatuan Snr and four other family members for their alleged role in the massacre, and are waiting for the justice department to decide whether to charge them in court.

The savagery of the murders, which included the deliberate targeting and execution of at least 30 journalists, has shocked this Catholic nation as well as the international community.

Police allege Ampatuan Jnr and 100 of his gunmen shot dead the occupants of a convoy that included relatives of his rival for the post of Maguindanao governor in next year's elections, as well as the group of journalists.

The rival, Esmael Mangudadatu, said the killings were carried out to stop him from running for office.

Ampatuan Jnr and Snr were members of President Gloria Arroyo's ruling coalition until being expelled last week because of the killings.

Maguindanao is part of Mindanao island, where an insurgency by Muslim rebels fighting for an independent homeland has claimed more than 150,000 lives since the late 1970s, according to military estimates.

Arroyo's government has used Muslim clans such as the Ampatuans to rule these areas, and allowed them to build up their own armies as part of a containment strategy against the insurgents.

However critics of the strategy have said this has created warlords who act outside the law, with the massacre just the most dramatic example.

Possible revenge attacks

Brawner said the extra military presence was needed to prevent further explosions of violence, including possible revenge attacks from the Mangudadatu clan, which is also known to have armed supporters.

Meanwhile, relatives of slain journalists on Wednesday demanded swift justice from Arroyo, who visited their wake in General Santos city, just a few hours' drive from the massacre site.

"I demand justice for my daughter. We should do to the Ampatuans what they did to her and her friends," said 90-year-old Maura Montano, whose daughter Marife of the Saksi News tabloid, was among those killed.

In Manila, Chief Superintendent Arturo Cacdac, head of the national crime laboratory, said investigators had so far autopsied 37 massacre victims, six of them women.

He said the majority of the victims were shot with M-16 automatic rifles or shotguns.

There was also indication that some of the women in the group were sexually assaulted, although no conclusive evidence of this has so far been gathered, according to Cacdac.