MANILA - The Philippines on Friday barred its top elected official in the south, his father and other relatives from leaving the country as it investigated the massacre of 57 people earlier this week.

Justice Secretary Agnes Devanadera told reporters that immigration offices had been told to prevent Zaldy Ampatuan, the governor of the autonomous region in Muslim Mindanao which covers six provinces, and other relatives from going abroad.

They are under investigation now and under surveillance, Devanadera told reporters. They are all considered suspects.

Zaldy's brother, Andal Ampatuan Jr, has been charged in connection with Monday's killings of rival clan members, journalists and witnesses.

Their father, Andal Ampatuan Sr, is the patriarch of the clan and widely believed to be one of the most powerful people in the lawless Mindanao region. He, Zaldy and six others are being investigated, Devanadera said.

President Gloria Macapagal Arroyo, a key political ally of the Ampatuans, has given the interior secretary permission to suspend all local officials in Maguindanao who may have a role in the crime, Cerge Remonde, the press secretary, told reporters.

Remonde said charges could be filed against Andal next week.

The army replaced a general and a colonel who headed infantry units in Maguindanao province and placed them under investigation for security lapses, military spokesman Lieutenant-Colonel Romeo Brawner said on Friday.

The military said about 400 assault rifles and two armored vehicles with heavy machineguns had been seized from the Ampatuans. Nearly 350 members of a civilian militia force are being held an army base in nearby South Cotabato province.

A politician of the rival Mangudadatu clan, whose wife, sisters and other relatives were among those killed, registered his candidacy for elections next year, the root cause of the feud.

Esmael Toto Mangudadatu said the massacre had not altered his plans to run for the post of governor of Maguindanao province, which has been controlled by the Ampatuans for decades.

Mangudadatu's 50-vehicle convoy to the office was escorted by soldiers and combat-trained police units, passing along the same highway where his wife's caravan, which included dozens of journalists, was stopped by about 100 armed men on Monday.

They were on the way to the election office to file Mangudadatu's candidacy papers. Fifty seven were shot and hacked to death and most of them buried in three shallow graves on a hillside off the highway.

The victims included 27 journalists and seven people who were not part of the convoy. Those seven were killed because they witnessed the crime.

Clan wars like the feud between the Mangudadatus and the Ampatuans are common in the southern Philippines. (Reporting by Manny Mogato; Editing by Nick Macfie)