Mrs Arroyo said she would not resign

House of Representatives minority leader Francis Escudero said the opposition bloc was considering pressing for Mrs Arroyo's impeachment.

Mrs Arroyo on Monday apologised to the nation, describing her action as a "lapse of judgement".

But she denied claims of trying to rig the poll, saying she would not quit.

Critics said a tape recording of a phone call between a woman sounding like her and an election commissioner was proof she tried to influence the vote.

"She [Mrs Arroyo] should ask herself if she still has the moral authority to lead the country," Mr Escudero told DZBB radio.

However, he said it would be better if the president resigned of her own accord.

Several other leading opposition politicians backed his call, vowing to pursue protests and legal steps against Mrs Arroyo.

Arroyo's defence

In Monday's televised address the president did not directly refer to the tape recording, which was released to the media three weeks ago.

Protests against Mrs Arroyo have been small-scale so far

But she did say she had spoken to an election commissioner about her share of the vote in the May 2004 poll.

"I was anxious to protect my votes and during that time had conversations with many people, including a Comelec (commission on elections) official," she said.

"My intent was not to influence the outcome of the election and it did not."

The president rejected calls to step down, saying the "outcome had been predicted by every major public opinion poll" and judged to be fair by international observers.

Telephoning an election official during the vote is not illegal in the Philippines, but the opposition is still likely to see it as a clear breach of conduct.

In the election, Mrs Arroyo beat the now-deceased film star Fernando Poe by more than a million votes.

In addition to the tape recording controversy, the president also faces separate allegations that members of her family took pay-offs from illegal gambling syndicates.