Afghanistan is likely to hold a runoff election to decide the country's new president, said some Afghan and Western officials, an outcome that would prolong the political uncertainty that has hurt U.S. efforts to beat back resurgent Taliban militants.

The United Nations-backed Afghan Electoral Complaints Commission on Thursday completed an audit of votes from the August first round of the election, which was tainted by allegations of widespread fraud. Afghanistan's Independent Election Commission will now subtract from the total count the votes disqualified by the ECC. Results are expected this weekend.

If enough votes are rejected, President Hamid Karzai's share could fall below the majority needed to avoid a runoff with top challenger Abdullah Abdullah.

Mr. Karzai's office in Kabul and Dr. Abdullah's team said separately Thursday that they were still expecting the president to emerge from the audit as the outright winner.

But other officials said to expect a second round. "A runoff is a likely scenario," Afghanistan's ambassador to the U.S., Said Tayeb Jawed, told a conference in Washington hosted by the U.S. Institute of Peace. "If that's what it is, everyone should work very hard to make that happen."