Lawmen believe that the target of the attack was Maguindanao Gov. Andal Ampatuan.

Mrs. Arroyo ordered authorities to put up a reward for any information that may lead to the arrest of the terrorists who carried out the attack.

"On the bombing in Maguindanao, targeted at the governor and which killed five people, I condemn this act of terrorism in the strongest possible terms as a crime against peace and humanity," Mrs. Arroyo said in her speech during the signing of the law abolishing the death penalty.

"The authorities must identify the perpetrators, launch a manhunt with the proper rewards, and bring them to justice," she added.

A bomb left in a parked car in a crowded market in Shariff Aguak, Maguindanao exploded on Friday morning, as the convoy of Ampatuan was passing by. Ampatuan was not hurt but five people were killed while 10 others were hurt in the blast.

Mrs. Arroyo expressed her sympathies to the families of the victims, and assured them of a firm and relentless administration of justice.

"We will never be intimidated by these treacherous acts and we shall fight terror as seriously as we embrace peace and development, solidarity among our law-abiding citizens, and our strategic alliances," Mrs. Arroyo said.

"This commitment stands firm and will not relent until the total defeat of terrorists in every part of the country," she added.

Meanwhile, police have arrested three people believed to be involved in Friday’s carbombing attack.

This developed as the death toll in the attack went up to six when four of the seven wounded perished while undergoing treatment in a hospital.

Senior Supt. Akmad Mamalinta, director of the Autonomous Region in Muslim Mindanao (ARMM) police, said the three suspects are now in police custody and are undergoing tactical interrogation.

"We have arrested three people linked to the bomb attack on Gov. Ampatuan. Their names cannot be disclosed yet as they are undergoing tactical investigation," Mamalinta said.

He said those arrested were local boys and suspected to be hired killers by former political opponents of the Ampatuans.

The Moro Islamic Liberation Front (MILF) has denied involvement in the attack against Ampatuan as two of its top officials issued a joint official statement condemning the blast.

Ustadz Omar Pasigan, chairman of Darul Ifta, and Ustadz Mohammad Muntasir, chairman of the MILF Committee on Da’wah, who both held portfolios with direct authority from Islam, issued the denial in the MILF website "Luwaran."

"This blast is the handiwork of insane people or persons of bloody-minded upbringing," Pasigan and Muntasir said in the statement.

"The mass murder of innocent persons has no basis in Islam," Pasigan said, adding, "Prophet Muhammad (Peace be upon him) said that whoever saves the life of one man is as if he saves the life of all mankind."

Muntasir denounced the blast as the handiwork of cowards, out to sow terror and intrigue in society.