Philippine President Gloria Macapagal-Arroyo has declared martial law in parts of a volatile southern province as security forces moved to arrest members of a local political clan linked to last week's gruesome massacre of 57 civilians.

Executive Secretary Eduardo Ermita on Saturday announced the proclamation of martial law in Maguindanao province, imposed by Arroyo on Dec. 4. Civil rights in the province will be suspended and the President is entitled to order troops to crush rebellion attempts to maintain public order and safety.

But Ermita said that there is no need to evacuate civilians in the area yet.

Armed Forces of the Philippines Chief of Staff Gen. Victor Ibrado said six infantry battalions, two mechanized battalions and a battalion-size of Special operations Command forces have moved in Maguindanao, enforcing the martial law.

Ibrado said the military recommended the martial law after noticing the massing of hundreds of armed militia loyal to a powerful political clan and feared that they might incite violence.

"Based on the reports that we received, there were a lot of groupings of armed group in different places in Maguindanao and they have plans to undertake hostile actions if ever the Ampatuans were taken into custody and we feel that this is a very imminent threat so we recommended for this proclamation," Ibrado said in a press conference.

The Ampatuans, who have ruled the province since 2001, are suspected of ordering the massacre of at least 57 unarmed civilians, including 22 women, who were on an election caravan to witness one of the family's political rival to be registered as governor candidate in next year's election.

Authorities have arrested and charged Andal Ampatuan Jr., mayor of Datu Unsay town of Maguindanao, as the prime suspect in the massacre. Thousands of troops moved in Maguindanao since last week and the authorities have ordered the relief of over a thousand local law enforcement personnel and started to disarm Ampatuan family's private armies.

After Arroyo imposed the martial law, security forces on Saturday dawn held two other prominent members of the Ampatuan clan -- Andal Ampatuan Sr., a three-term governor of Maguindanao, and his son Zaldy Ampatuan, incumbent governor of the Autonomous Region in Muslim Mindanao (ARMM), -- from the family's mansions in the Maguindanao provincial capital of Shariff Aguak.

Officials to head the Maguindanao province and the ARMM will be determined soon. A senior cabinet official said civilian authority, not a military governor, is to be installed.