MANILA, December 8, 2009 (AFP) - Rights group Amnesty International urged the Philippines Tuesday to establish a "clear and short timetable" to end martial law imposed on a southern province where a political massacre left 57 dead.

Amnesty said it was not so far aware of any serious rights violations since President Gloria Arroyo imposed martial law on Maguindanao province Friday.

But it raised concerns about dozens of arbitrary arrests by troops, said 2,000 people had fled their homes since martial law was imposed and warned the security measures exacerbated the potential for human rights violations.

"(Arroyo) should immediately establish a clear and short timetable for an end to martial law," said Sam Zafiri, Amnesty's regional director, after visiting the province.

"Every day of heavy military deployment increases the risk of human rights violations."

Zafiri also called on Arroyo to revoke a 2006 decree that allowed the use of paramilitary forces by local officials in counter-insurgency operations, a strategy that backfired on the government in Maguindanao.

"Local strongmen have used these forces as private armies," Safiri said. "The way the government allowed it to be implemented was a recipe for disaster."

One of the government's reasons for imposing martial law was to dismantle a 3,000-member militia force under the control of the Ampatuan clan, whose members are accused of masterminding the November 23 massacre.

Arroyo, in a report to Congress on Monday. defended the martial law move, saying the Ampatuans and their militiamen threatened to attack if any of the clan leaders were arrested.

The Philippines' Congress will debate the measure on Wednesday, amid public fears the unpopular Arroyo may use martial law as an excuse to hold on to power.

Authorities said 62 people have been arrested during the martial law sweep, including five Ampatuan clan leaders.

Troops have also seized large caches of firearms hidden in the clan's properties, including anti-tank weapons and armoured personnel carriers.

One clan member, Andal Ampatuan Jr., has been charged with 25 counts of murder over the massacre. Police allege he and his gunmen abducted and killed female relatives of a political rival, plus a group of journalists.