Several gunmen suspected of involvement in the Philippines election-related massacre of 57 people including politicians and journalists have been arrested.

"We don't have an exact number (of those arrested), but our policemen in the area have arrested several," the Philippines Police Chief Director General Jesus Verzosa was quoted by AFP as saying on a local radio.

National police chief identified the suspects as militiamen under the control of powerful Filipino politician Andal Ampatuan Jr.

Ampatuan is accused of masterminding Monday's killings in the southern province of Maguindanao. The Police Chief noted that Secretary Jesus Dureza, President Gloria Arroyo's adviser on the southern island of Mindanao, would accompany Ampatuan to submit to an investigation.

The victims were snatched by nearly 100 Ampatuan gunmen as they were traveling in a convoy to nominate Esmael Mangudadatu as the opposition candidate for provincial governor in next year's elections.

The bullet-ridden bodies had been buried in shallow graves in a remote farming area on Mindanao Island. The death toll from the political killing later rose to 57 people, including 12 journalists.

Political violence is common in the Philippines, where more than one million unlicensed guns flow freely among a population of 92 million, and dozens of people are murdered during each election season.

RZS/SS/RE