Witness claims to have seen Andal Ampatuan Jr ordering killings and personally firing at convoy of journalists and political rivals

A senior member of a clan that has ruled a southern Philippine province for years was directly involved in the massacre of 57 people, including the wife and sisters of a political rival and dozens of journalists, the country's justice secretary said today .

Andal Ampatuan Jr, mayor of a town in the hill region where the killings occurred, and son of the governor of Maguindanao, whose family has close links to the country's president, Gloria Macapagal-Arroyo, has been charged with mass murder for allegedly organising the killings.

Speaking in Manila, the federal justice minister, Agnes Devanadera, said a witness had testified that Ampatuan was at the scene and ordered the killings. "He saw the carnage," she said. Asked whether the witness saw Ampatuan firing a weapon, she added: "Yes."

The man was among the militia members and local security forces who took part in the massacre, she added.

Devanadera said the bodies of many of the 20-plus female victims had been sexually mutilated, although it was not known if the women had been raped.

In a crime that has shocked the region, a convoy of vehicles carrying supporters of a political rival and reporters was ambushed on Monday. The passengers were shot at close range and dumped in mass graves. Investigators believe 15 of those killed were bystanders shot to eliminate witnesses. Up to 30 were journalists or media workers.

Among the dead were the wife and two sisters of Ismael Mangudadatu, who plans to run against the younger Ampatuan for the governorship in elections next year.

Following threats, Mangudadatu decided not to travel with the convoy to an electoral office to file candidacy papers. He believed that his relatives, as women, would be spared violence.

Separately, Mangudadatu said witnesses who escaped the massacre saw Ampatuan personally flag down the caravan and slap his wife.

Ampatuan handed himself in yesterday, following threats that his family compound faced military assault, and is in jail in Manila. He has insisted on his innocence, saying that at the time he was in his office at the town where he serves as mayor.

Mangudadatu registered his candidacy today, leading another convoy, guarded by soldiers and hundreds of supporters, along the same route. "Only death can stop me from running," he said as he submitted the papers. Following the massacre, Arroyo expelled Ampatuan family members from her party and pledged justice for the victims. Ampatuan Sr had seemingly been grooming his son to take over as provincial governor.

Maguindanao is a province on the southern island of Mindanao, an often lawless region where a decades-long insurgency by Muslim groups seeking independence within the mainly Catholic country has killed tens of thousands of people. Several of these organisations have previously kidnapped and murdered foreign nationals, as well as many more local people. Ampatuan has blamed the massacre on one of the Muslim groups, the Moro Islamic Liberation Front. It has denied this, and the government says there is no evidence of rebel involvement.