Police named 100 government militiamen as additional suspects in the Philippines' worst political massacre Wednesday as prosecutors filed rebellion charges against a powerful clan accused of ordering the brutal attack on a rival's campaign convoy.

President Gloria Macapagal Arroyo's top Cabinet officials appeared before lawmakers to defend her proclamation of martial law in southern Maguindanao province, where 57 people were killed, some left sprawled on the ground and others buried in mass graves.

Critics called the martial law declaration a dangerous precedent, but Cabinet members said it was needed to stave off a rebellion by the Ampatuan family, the main suspects in the Nov. 23 killings, and their thousands-strong private armies ready to fight the government.

The Ampatuan clan gained notoriety for intimidating political opponents and protecting their turf, which until the massacre made any action against them impossible.

The head of the Philippines' independent Commission on Human Rights, Leila de Lima, said her office had received a letter from anonymous citizens blaming the Ampatuans for at least 200 other killings in the area in the past decade. De Lima cautioned that the allegations had not been validated and did not provide details but said she would investigate.

She said her office had asked the elder Ampatuan to comment on the allegations but he never responded.

Witnesses in custody have identified Andal Ampatuan Jr., a scion of the clan, as leader of a group of government militiamen who attacked a rival's convoy in Ampatuan township, said national police chief Jesus Verzosa.

The dead included 30 journalists and their staff.

According to the witnesses, Ampatuan himself shot some of the victims. The bodies bore bullet wounds in the mouth and chest fired from close range, Verzosa said.

Police said the bodies of some of the 21 female victims were mutilated, including their sexual organs. Authorities earlier had said at least five women may have been raped.

Among the total of 161 murder suspects are about 100 newly identified militiamen, only two of them in custody _ Esmael Kanapa and Takpan Dilon of the Civilian Volunteer Organization, a police auxiliary force, police officials said Wednesday.

Government-sponsored militias have become a fixture in many Philippine provinces plagued by Muslim and communist rebellions and by bandits. Over the years, the over-stretched military and police have been arming civilian volunteers as a back-up force. In areas like Maguindanao, some have become de facto private armies on the payroll of local political warlords.