WASHINGTON: A senior aide to Afghan President Hamid Karzai has for the first time conceded that disputed elections could enter a second round and pushed to hold the run-off quickly.

Said Tayeb Jawad, Afghanistan's ambassador to the United States, said Thursday he has not personally spoken to election authorities who are expected to make an announcement within days.

But Jawad, who has served as Karzai's chief of staff and press secretary, became the first member of his circle to speak publicly of plans for a new vote after Western-led allegations of major fraud in the August 20 polls.

"A run-off is a likely scenario," Jawad said at the US Institute of Peace.

"If that's what it is, everyone should work very hard to make that happen."

Jawad said the next round of presidential elections should be held quickly, charging that a delay would create headaches for other nations -- including the United States, as it mulls sending more troops to fight Taliban insurgents. Related article: Afghan govt's "to do" list

"The constitution requires a run-off be done within two weeks but that's impossible. So four weeks will push it into early November and that's the latest that it will happen because after that it will be extremely cold, especially in northern Afghanistan," Jawad said.

"But if it's delayed to spring, this is clearly a recipe for disaster -- this creates a lot of confusion, a lot of indecisiveness and also further complicated relations" with the outside world, he added.

Karzai has passionately rejected charges of widespread irregularities, testing the patience of Western nations that were his key backers after the US-led military operation in 2001 that toppled the Taliban regime.

European Union observers said a quarter of all votes, or 1.5 billion ballots, were suspect.

Afghan election authorities are reviewing disputed ballots. A senior US official, speaking on condition of anonymity, expected a final announcement on Sunday or Monday.

Karzai's chief rival, urbane former foreign minister Abdullah Abdullah, said in Kabul that he was hopeful investigations into ballot-stuffing allegations would result in a run-off.

But Abdullah warned that if a run-off were not called, "those who are behind the fraud and tolerate fraud will be responsible for the consequences."

Fellow candidate Ashraf Ghani, a former World Bank official, said on a visit to Washington that Karzai and Abdullah so distrusted each other and election authorities that only a deal between the two could break the impasse.

"When legitimacy is called into question, repeating an election with the same people and the same institutions... becomes problematic," he told us public broadcaster PBS.

But Jawad played down the possibility of a coalition government, saying both sides would then be inclined to make appointments based on loyalty rather than competence.

Karzai, speaking earlier this week to the US television network ABC, branded charges of systematic fraud as "totally fabricated" and "politically instigated."

Jawad also rejected criticism of the polls, saying that "if fraud delegitimizes the process, as of course it does, too much interference by outside or inside sources also delegitimizes the process."

The ambassador was unusually open about Karzai's disagreements with President Barack Obama, who has been cooler toward the Afghan leader than his predecessor, George W. Bush.

While describing relations as improved, Jawad said that early in the Obama administration, "there was some oversimplication of the issues" and "even there was this lack of knowledge" about Afghanistan's complex ethnic patchwork.

"But after awhile this has changed and everybody realized it's not really as simple as that, just getting rid of a leader of a country you don't like," he said.

Obama has made the fight against Islamic extremism a chief focus of his young presidency.

He signed a five-year, 7.5-billion-dollar development package for violence-torn neighbor Pakistan on Thursday as he weighs a decision on whether to send tens of thousands more US troops to Afghanistan.