Opposition candidate Abdullah Abdullah leaves in his car after attending a gathering held in his support in Kabul September 27, 2009. [Agencies]

KABUL: President Hamid Karzai's chief political rival agreed Wednesday to stand in the Nov. 7 run-off election, setting the stage for a high-stakes showdown in the face of Taliban threats and approaching winter snows.

Those findings showed Karzai failed to win the 50 percent required to avoid a run-off.

Abdullah said he telephoned Karzai to thank him for agreeing to the second round ballot.

"We are completely ready for the second round at the date which has been announced," Abdullah said.

He called on Afghan officials to organize a "free, fair and credible election" with enough security encourage people to turn out and vote.

Abdullah's declaration sets the stage for an election which UN Secretary-General Ban Ki-moon said it will be a "huge challenge" to pull off without repeating the widespread fraud that marred the first-round balloting.

Karzai's capitulation Tuesday was a relief to American officials and averted a constitutional crisis. But new balloting carries with it the risk of low turnout or another round of wholesale ballot-stuffing and voter intimidation.

That would bring the Obama administration no closer to its goal of a credible, legitimate Afghan government necessary to win public support in the US for the war in Afghanistan and reverse the Taliban rise.

If the election goes relatively well, it's unclear that a second-round win by Karzai, widely considered the favorite, would erase the stain brought on his leadership by widespread fraud in the first balloting Aug. 20.

Holding the poll as the country enters its cold season poses additional challenges, both for transporting ballots and drawing voters. US and Afghan forces also must provide security for the balloting to prevent a repeat of Taliban attacks in August that killed dozens. In some areas, militants cut off the ink-marked fingers of people who had voted.