Mr Anwar is on trial for corruption. Charges relating to alleged sexual offences were dropped last month.

Wan Azizah Ismail said she might run against the prime minister in his own constituency in the northern state of Kedah.

"I'm keeping that option open," she said in comments to the Associated Press news agency.

Wan Azizah set up her own movement last December, saying it would press for economic, social and political reform.

Correspondents say that if Dr Mahathir loses his seat, he would no longer be able to remain prime minister.

Earlier, a coalition of opposition parties and non-government groups announced they would mount a concerted challenge to the prime minister.

The 25-party Coalition for People's Democracy - which includes Wan Azizah's movement - says it is discussing a common election platform.

Dr Mahathir has to call elections by April next year.

Summons served

On Friday, lawyers for Anwar Ibrahim served a summons for slander on the Prime Minister, Mahathir Mohamad.

Anwar Ibrahim's private prosecution for slander is claiming $26m in damages for comments made by the prime minister.

Lawyers say he is also considering action against some news organisations which carried Dr Mahathir's comments, made shortly after Mr Anwar was arrested on sodomy and corruption charges.

Mr Anwar's lawyers say that the prime minister's remarks caused "agony and pain" and "colossal damage" to the jailed politician's reputation.

At the news conference on 22 September 1998 Dr Mahathir graphically described Anwar's alleged acts of sodomy, a crime in Malaysia.

Mr Anwar's lawyer said his client was not filing defamation suits just for possible financial benefit: "Money is not the issue. Justice is."

Defence case

The trial of Mr Anwar on corruption charges resumes next week after a 10-day break with the opening of the case for the defence.

Mr Anwar has said he wants to call Dr Mahathir and several other cabinet members to give evidence.

Mr Anwar maintains the charges against him are all part of a political conspiracy to oust him from power.