SHARIFF AGUAK, Maguindanao, Philippines?(UPDATE) Police on Monday said that militiamen loyal to the powerful Muslim clan of Ampatuan attacked security forces after martial law was imposed in their province following a brutal massacre.

Supporters of the Ampatuan clan?whose leaders are key suspects in the November mass murders?fired on police on Sunday, two days after President Gloria Macapagal-Arroyo declared martial law on Maguindanao province, authorities said.

Police commandos were on routine patrol searching for illegal weapons when they were attacked, triggering a 10-minute clash.

"Suddenly they were fired upon and there was an exchange of gunfire. They were not able to move so they called in reinforcements," national police chief Director General Jesus Verzosa said.

The commander of military forces in Maguindanao, Lieutenant General Raymundo Ferrer, said Monday that troops were hunting down 3,000 Ampatuan followers who had escaped to the hills before martial law was imposed.

"The number would not be less than 3,000," Ferrer told dzBB radio in Manila. "These (militiamen) are in hiding with their weapons. They have said they will fight and there are many of them."

Interior Secretary Ronaldo Puno said the militiamen were formerly under government control and were effectively controlled by the Ampatuans, who had once helped Arroyo against Muslim separatist insurgents in the area.

"They have severed themselves from the chain of command and lawful authorities that have been supervising them," Puno said.

Members of the Ampatuan family, which has ruled the province for a decade, are accused of orchestrating the November 23 massacre of 57 people, including members of a rival family and 30 journalists.

Arroyo said she was forced to impose martial law after Ampatuan forces threatened to attack if the leaders were taken into custody.

Thousands of troops and police have taken over the province since martial law was declared and raids on Ampatuan properties have yielded a vast array of military hardware.

Puno on Monday said these include a total of 883 firearms, 430,000 rounds of ammunition, as well as anti-tank weapons and armored personnel carriers.

As of Sunday, 62 people had been arrested, including clan patriarch Andal Ampatuan Sr. and four other clan members. His son, Andal Ampatuan Jr., is being held in a Manila jail charged with 25 counts of murder, while other leaders face charges of rebellion.

Police said the murders were carried out to prevent a rival politician, Esmael Mangudadatu, from challenging Ampatuan Jr. for the governor's post in an election in May.

Ampatuan Sr. has ruled the province as governor since 2001 and was grooming his son to take his place. Other clan members were appointed to high provincial posts in Maguindanao, an impoverished province of 700,000 people.

General Ferrer conceded the clan was able to maintain a private army because the government had used it in the past to help contain the Muslim separatist rebellion that has claimed more than 150,000 lives since the 1970s.

"The problem was they went beyond government control. The family controlled them and they were used for evil deeds," Ferrer said.

He said that despite military presence, fear of the Ampatuans and their forces remain deep-seated.

"The (belief) here is that when you speak against the Ampatuans, you will not last a day, and you will never be found," Ferrer said.

Puno said that prior to martial law, the local courts, because they were either cowed by the Ampatuans or were protecting them, refused to issue warrants of arrests against clan members.