The United States vowed to support the next Afghan president, as White House advisers said fresh election turmoil would not complicate a US decision on whether to send more troops there.

Secretary of State Hillary Clinton acknowledged presidential challenger Abdullah Abdullah's decision to withdraw from the runoff scheduled for November 7, and said Washington was ready to work with the leader of the next Afghan administration.

She also urged authorities in Afghanistan to quickly bring the drawn-out election process to a close, now that Abdullah has removed himself from the contentious presidential race.

"It is now a matter for the Afghan authorities to decide on a way ahead that brings this electoral process to a conclusion in line with the Afghan constitution," she said.

Clinton praised Abdullah's "dignified and constructive campaign" and urged him to continue to work "on behalf of the security and prosperity of the people of Afghanistan."

But she indicated that the United States was ready to move past the scandal-plagued Afghan elections, saying that Washington "will support the next president and the people of Afghanistan, who seek and deserve a better future."

Meanwhile, White House advisers said the sudden pullout of President Hamid Karzai's challenger would not affect US President Barack Obama's process of deciding whether to send more US troops to the war-torn country.

Top presidential adviser David Axelrod said he expected the US president would "make a decision within weeks," on war commander General Stanley McChrystal's request for 40,000 more counter-insurgency troops.

"Mr Abdullah... has made a political decision to withdraw from this contest. And that doesn't markedly change the situation," Axelrod told CBS television.

"Every poll that had been taken there suggested that he was likely to be defeated anyway. So we are going to deal with the government" of the incumbent, Karzai, Axelrod said.

An election commission found that about a quarter of all votes cast in the first round of balloting in Afghanistan were fraudulent.

Revised results showed that Karzai fell just below the 50 percent threshold needed for an outright election victory, forcing the runoff which was to have been held later this week.

Abdullah, who earned just over 30 percent in the first round election voting, said he pulled out of the second round amid concerns of a repeat of the massive fraud and vote-rigging that marred earlier balloting.

Leading Republican lawmaker John Boehner told CNN television that Abdullah's withdrawal would "not hamper our decision with regard to Afghanistan."

Boehner also urged Obama, who has spent the last several weeks deliberating the best strategy going forward in Afghanistan, to decide soon.

"The longer this decision hangs, the more jeopardy and the more danger our troops on the ground there are in the middle of," said Boehner, who is the House minority leader.

"I think everyone expected that President Karzai was going to be re-elected. So Dr Abdullah's exit from this race, I think, really says more about the fact that he knew he wasn't going to win."

US diplomats and troops in Afghanistan say they need a military "surge" there to succeed and stand ready to work with Karzai, a US lawmaker said after a visit there.

Republican Representative Duncan Hunter, who sits on the House Armed Services Committee, told AFP by telephone that US personnel were "unanimous" on both fronts in a series of at least 10 meetings in the war-torn country.

"Everybody seems very confident, very excited. Everybody thinks that they can win it, we can win it, we can hand it over to the Afghans, and we can get out of there," he said during a brief stop in Dubai.

But US officials underlined that "we've got to have the surge to do what we've been asked to do. Nothing's going to work without more security. If we have the security, it's going to work," said Hunter.

White House adviser Valerie Jarrett agreed that Abdullah's exit posed no obstacle, but said Obama still needs to carefully deliberate with his top aides on the way forward in Afghanistan.

"We don't think that it's going to add a complication to the strategy. It's up to the Afghan people and their authorities to decide how to proceed going forward," she told ABC television.

"Before (Obama) puts our men and women in harm's way, he wants to make absolutely sure that he has a strategy," Jarrett said.

This video is from Al Jazeera, broadcast Sunday, Nov. 1, 2009.

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With AFP.