MANILA - Several gunmen linked to a powerful Philippine politician were arrested Thursday over the election-related massacre of at least 57 people, the country's police chief said.

"We don't have an exact number (of those arrested), but our policemen in the area have arrested several," Philippine National Police Director General Jesus Verzosa said on DZBB radio.

He identified the suspects as militiamen under the control of Andal Ampatuan Jnr, who is accused of masterminding Monday's killings in the southern province of Maguindanao.

"Andal Ampatuan Jnr is a suspect. He has sent feelers and Secretary Dureza will accompany him to submit to an investigation," Verzosa said, referring to President Gloria Arroyo's adviser on the southern island of Mindanao.

The massacre occurred after about 100 Ampatuan gunmen allegedly abducted a convoy of aides and relatives of a rival politician, Esmael Mangudadatu, plus a group of journalists.

The victims were snatched as they were travelling in a six-vehicle convoy to nominate Mangudadatu as the opposition candidate for provincial governor in next year's elections.

They were shot at close range, some with their hands tied behind their backs, and dumped or buried in shallow graves on a remote farming road close to a town bearing the Ampatuan name.

Fifty-seven bodies have been recovered so far, and police are still searching for more potential victims.

Ampatuan Snr had been grooming his son, currently a local mayor, to take over as governor of Maguindanao.

The victims' relatives alleged the Ampatuans organised the murders so that Mangudadatu would not run for that post.

Thursday's actions by the police were the first arrests in relation to the massacre.