MANILA - Former president Joseph Estrada vowed Monday that there would be no repeat of last week's political massacre under his watch, as he registered to run in next year's presidential elections.

Estrada was one of three opposition candidates to file their nominations for the May presidential poll amid a continued outpouring of national grief over the horrifying slaughter of 57 people in the volatile south of the country.

"That will not happen in my administration. I will never tolerate warlordism," Estrada said of the killings.

A local mayor who was a member of President Gloria Arroyo's coalition, Andal Ampatuan Jr., has been charged with murder over the November 23 killings, and other members of his powerful clan have been named as suspects.

The victims' relatives allege Ampatuan Jr. organized the murders to stop a rival politician from running against him for the post of governor of Maguindano province next year.

The other significant presidential contender to register his candidacy on the penultimate day for filing was billionaire property developer Manny Villar, who is running second in popularity polls behind Senator Benigno Aquino.

Televangelist Eddie Villanueva was the other opposition candidate to register.

Tuesday is the final day for registering for the presidential and congressional elections and the other main interest was on whether Arroyo would register to run for a seat in the lower house of parliament.

Her lawyer, Romulo Macalintal, said Arroyo was "seriously considering" running in her home province of Pampanga. Critics of Arroyo have hit out at her much-speculated plans to run in Congress.

They say Arroyo and her allies may want to change the constitution to create a system of government where a prime minister, rather than a president, would rule the country and she would be the first to take that position.

In the last national survey of preferred presidential candidates conducted last month, Aquino had a clear lead with 44 percent of the vote, while Villar was second with 19 percent.

Estrada was in fourth place with 11 percent while Arroyo's designated successor, former defence secretary Gilberto Teodoro had just two percent support.

Estrada, a former movie star, was elected president in 1998 but was ousted by a military-backed popular uprising in 2001 amid allegations of massive graft over which he was later found guilty and jailed. Estrada said Monday he would do nothing differently from his first scandal-tainted term.

"There will be no changes. I will continue with my pro-poor programmes, food security, peace and order and go against graft and corruption," he said.

Estrada brushed aside his own 2007 conviction for graft and corruption which resulted in his being sentenced to life imprisonment. Arroyo, in an apparent concession to Estrada's supporters, later commuted his sentence.

"I forgot. I believe I have not done anything wrong," he said when asked what he learned from his 2001 ouster. Estrada also said legal experts had assured him that he was still eligible to run even though the constitution barred a president for running for re-election. "I was only there for two and a half years so I can still run to finish my term," he told reporters.