The Philippine President, Gloria Arroyo, has said "no effort will be spared" in the hunt for those behind what is believed to have been a politically-driven massacre in the south of the country.
Local media reports on Tuesday said at least 39 were believed to have been killed in the attack, up from an initial death toll of 22.
The victims were part of a group of 40 people abducted in Maguindanao province by around 100 armed men.
Among those killed were the wife and family members of a local politician, as well as journalists.
The army has linked the killings to political rivalries ahead of next year's local elections.
In a televised address to the nation on Tuesday afternoon, Arroyo said she was determined that those behind the killings would be held "accountable to the full limit of the law".
Extrajudicial killings
The killing of political rivals and journalists is common in the Philippines, so much so that the government set up two bodies to investigate the practice.
The police-led task force Usig confirmed 116 cases of political murder between 2001 and 2007. Twelve suspects were arrested but no convictions have been made.
The Melo Commission in 2007 found 136 political murders, with strong evidence implicating the armed forces in the killing of those perceived to be enemies of the state.
"The chief of staff has ordered the establishment of check points and choke points and as of last night, the military elements were in place to preserve peace in the areas. Additional troops have also been deployed to the area last night to further secure the area," she said.
Earlier officials in the president's office said she had ordered a state of emergency in the area, following what they said was the worst political violence seen in the country in recent history.
Lieutenant-Colonel Romeo Brawner, a spokesman for the Philippines military, said about 500 more soldiers had been sent to Maguindanao province on the island of Mindanao "to go after the criminals" believed to be behind the killings.
He said the troops were under orders to arrest the followers of Andal Ampatuan, the incumbent governor suspected of being behind the killings, following the abduction of more than 40 journalists and supporters of his rival, Esmael Mangudadatu.
"We maintain the Ampatuans are the suspects," Brawner told the AFP news agency.
On Monday the military said 22 bodies - most female, some beheaded and mutilated - had been found in a mass grave in a remote mountainous area and the number was likely to rise as soldiers dug further at the site.
President's ally
Al Jazeera's Marga Ortigas, reporting from the Philippines, said Ampatuan is known to be closely-associated to the government and a close ally of Arroyo so people are watching to see what action the government will take.
Ampatuan is seen to have delivered the votes that swung the 2004 elections in Arroyo's favor, so people in the province fear he may not be punished if he is found to be behind the killings, our correspondent said.
Meanwhile Mangudadatu, whose family members, including his wife, were among those killed according to the military, told local radio that at least four people had survived the attack.
He said the survivors were safe under his care and "will come out at the right time".
On Monday Mangudadatu told local television network ABS-CBN that he had been warned about the dangers of standing for the governorship against Ampatuan, the incumbent and the head of a powerful rival family.
Mangudadatu said he stayed behind in the capital Manila and sent his wife, Genalyn Tiamzon-Mangudadatu, to file his nomination in Maguindanao on his behalf.
Officials said about 100 gunmen stopped members of the Mangudadatu family, lawyers and about a dozen local journalists on a highway on Monday and herded about 40 people away at gunpoint.
The southern Philippines is riven by clan rivalries, including one between the Mangudadatus and the Ampatuans.
PHOTO CAPTION
Philippine soldiers patrol the streets of Manila.
Al-Jazeera