"We're now told [Abdullah] is in intensive meetings; he is still making up his mind."

The Associated Press later quoted Satar Murad, the campaign manager, as saying Abdullah "as of now" planned to call for a boycott of the upcoming runoff, although he said Abdullah might still change his mind.

Possible boycott

Abdullah is said to be keen to halt the runoff in order that it will be delayed until next spring.

In depth

 Watch the full interview with Peter Galbraith 
 Video: Taliban warns against runoff
 Video: Afghans dismiss runoff vote
 Inside Story: The election runoff
 Blogs: That's democracy for you
 Blogs: Afghan election chaos: what the law says
Hillary Clinton, the US secretary of state, said that should Abdullah boycott the vote, the legitimacy of the elections would not be affected.

"I don't think it has anything to do with the legitimacy of the election," she said, in response to a question on the issue at a press conference in Israel.

"We see that happen in our own country where, for whatever combination of reasons, one of the candidates decides not to go forward."

The first round of Afghanistan's elections on August 20 was so badly affected by ballot-box stuffing and distorted tallies that more than one million votes were thrown out.

The fraud pushed Hamid Karzai, the president, below the required 50 per cent margin needed to win, forcing the country into a second round to be held on November 7.

Abdullah has accused the country's electoral commission of being complicit in the fraud.

Abdullah's conditions for the runoff to take place included the dismissal of Azizullah Ludin, the government-appointed co-ordinator, to ensure a fair vote.

But both the Karzai campaign and the election commission have said that Ludin will not step down.

Our correspondent said Abdullah's list of conditions included "stringent" demands involving both the government and the election body involved in organising the polls.

"The only one of his conditions that has been met is a demand for more accredited observers from the Abdullah camp and they will give him 20,000 accreditations," Hull said.

"But that is the only one and that is what puts him in a difficult position of deciding whether to participate given that his own minimum requirements have not been met."

Troop deployment

The growing uncertainty over Abdullah's participation comes as the US president continues consultations on further troop deployments to Afghanistan.

Barack Obama reviewed his options with the joint chiefs of staff - which includes the service chiefs from the army, navy, air force and marines - in Washington on Friday, his seventh such meeting.

General Stanley McChrystal, the leader of US and Nato forces in Afghanistan, has requested 40,000 more troops, giving warning on the deteriorating situation in Afghanistan.

But the joint chiefs of staff did not make recommendations to Obama about troop levels, an unnamed senior administration official was quoted by the Associated Press as saying.

The Washington Post newspaper reported, quoting US officials, that Obama asked the commanders to provide him with more options for troop levels.

Some of the alternatives would allow Obama to send fewer new troops than the number sought by McChrystal, one official said.

Bush's warning

Obama is expected to receive several options from the Pentagon about troop levels next week, according to the two officials.

"[The Taliban] attack political, financial and diplomatic targets because they hate our way of life and they hate our vision for freedom and human rights and human dignity and prosperity and peace"

George W Bush, former US president

Before he can determine troop levels, Obama's advisers have said, he must decide whether to embrace a strategy focused heavily on counterinsurgency, which would require additional forces to protect population centres, or one that makes counterterrorism the main focus of US efforts in the country, which would rely on relatively fewer American troops.

Against this backdrop, George W Bush, the former US president, said on Saturday that the war against the Taliban must be won to stop a return to "brutal tyranny" in Afghanistan.

In a speech to a leadership conference in New Delhi, the Indian capital, he said defeating the anti-government fighters was "necessary for stability" and peace both in the region and globally.

"If the Taliban, al-Qaeda and their extremist allies were allowed to take over Afghanistan again, they would have a safe haven and the Afghan people, particularly the Afghan women, would face a return to a brutal tyranny," he said.

"This region and the world would face serious threats."

Bush said both the US and India were "involved in an ideological struggle against extremists who murder the innocent to advance a dark vision of extremism and control".

He said "they attack political, financial and diplomatic targets because they hate our way of life and they hate our vision for freedom and  human rights and human dignity and prosperity and peace".