President Hamid Karzai's chief political rival agreed Wednesday to take part in the Nov. 7 runoff election, cementing the stage for a high-stakes showdown in the face of Taliban threats and approaching winter snows.

Ex-Foreign Minister Abdullah Abdullah made his comment to reporters one day after Karzai bowed to intense U.S. and international pressure and accepted findings of a U.N.-backed panel that there had been massive fraud on his behalf in the Aug. 20 vote. Those findings showed Karzai failed to win the 50 percent required to avoid a runoff.

As part of efforts to avert cheating in the upcoming ballot, election officials have fired 200 district election chiefs following complaints by candidates or observers about misconduct in their regions, the U.N. said last week. It was not immediately known how many posts in total there were.

SLIDESHOW: Presidential Runoff Ordered

The country's electoral crisis has comes as the Washington debates its way forward in a war that entered its ninth year this month.

Holding the second round of polling as Afghanistan enters its winter season poses serious challenges, both for drawing voters and distributing ballots nationwide, which the U.N. said would begin Thursday. Abdullah said U.S. and Afghan forces also must provide security to prevent a repeat of a wave of Taliban attacks in August that killed dozens. In some areas, militants cut off the ink-marked fingers of people who had voted.

Voters "are taking a risk in some parts of the country and they should be confident that that risk is worthwhile," said Abdullah, who said he called Karzai to thank him for agreeing to hold the second-round. "I would like to see that our people are participating without an environment and atmosphere of fear and intimidation."

But he conceded security was far from perfect. "There are some circumstances that we cannot change in the coming 15 days, like areas which Taliban can threaten the people," Abdullah said.

Abdullah's declaration sets the stage for an election that U.N. Secretary-General Ban Ki-moon said would be a "huge challenge" to pull off without repeating the widespread fraud that marred the first-round balloting. The world body has set aside more than $20 million to support the poll, according to the U.N. spokesman in Kabul, Aleem Siddique.

Finding replacements for election workers implicated in fraud will be difficult. The government had to scramble this summer to recruit enough election officials and poll workers, especially at voting stations for women. It's unclear if they would be able to fill open posts with better-qualified people.

"It is hard to see how a second round can be credible unless women's security and access to the polls is dramatically improved," said Rachel Reid, a researcher with Human Rights Watch in Kabul.

The Independent Election Commission, the Afghan body that runs elections, must also finalize the list of polling stations. Much of the fraud in the August balloting came through ballots that arrived from so-called "ghost polling stations" that never opened because they were in dangerous areas.

But closing the questionable stations would prevent voters in those areas from casting ballots. Kai Eide, the U.N. chief in Afghanistan, has said he worked to open the stations to avoid disenfranchising voters.

Abdullah said Wednesday that he is preparing a list of conditions that his team wants election organizers to commit to in order to have a fair vote. He said he would be open to negotiating the conditions, but would not accept an election organized on the same terms as the August vote.

"I will be flexible, but I will be serious about this because, after all, it is the transparency and fairness of the elections which will decide the outcome," he said.

Karzai's capitulation Tuesday was a relief to the Obama administration, which hopes the troubled nation has taken one step closer toward a credible, legitimate government necessary to win public support in the U.S. for the war and reverse Taliban gains. The U.S. military reported one of its troops was killed in a bomb attack in the south Tuesday, bringing the total number of Americans killed in October to 30.

Karzai announced the decision Tuesday after a day of intensive talks with U.S. Sen. John Kerry, chairman of the Senate Foreign Relations Committee. Later, in a telephone interview from Dubai with The Associated Press, Kerry described the evolution in Karzai's thinking.

"President Karzai really deeply believes he had won the election and ... that the international community was kind of conspiring to push for a different outcome," Kerry said. "He had people within his government, people within the election commission who felt they were being insulted about putting together a faulty election process."

"There were a lot of very deep feelings about Afghanistan's right to run its election, its competency in running it," Kerry said.