The Philippine police chief said Thursday policemen have arrested several gunmen linked to Monday's political massacre in the southern Philippine province of Maguindanao that has left at least 57 people killed.

Philippine National Police Director General Jesus Verzosa told dzBB Radio that the suspects are militiamen belonging to Datu Unsay Mayor Andal Ampatuan Jr., who is the prime suspect in the election-linked massacre.

National Police Spokesman Chief Superintendent Leonardo Espina said on Wednesday initial reports indicated the influential Maguindanao Governor Andal Ampatuan Sr. and his son are behind the massacre.

Political violence is not uncommon in the Philippines, especially in Muslim Mindanao, a region plagued by decades of insurgency battles and flooded with loose arms.

But the indiscriminate killing of women, working journalists, and civilian supporters shocked the nation and the international community.

Presidential Adviser on Mindanao Affairs Jesus Dureza said "specific actions" can be expected in 24 hours.