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Rahmat Gul, Associated Press
Afghan presidential candidate Abdullah Abdullah speaks during a press conference at his residence in Kabul, Afghanistan, Sunday, July 6, 2014. Abdullah, who has alleged massive fraud in last month's runoff vote, said he won't accept partial results if they're released as planned on Monday.

KABUL, Afghanistan — Afghanistan's election crisis deepened Sunday as the two presidential candidates sparred over the release of preliminary results and calls mounted for a broader investigation of suspect ballots amid allegations of massive fraud.

The impasse has threatened to undermine what the U.S. and its allies had hoped would be the country's first democratic transfer of authority after President Hamid Karzai agreed to step down after two terms as legally required.

Western officials were looking for a smooth transition to show progress ahead of the withdrawal of U.S. and allied combat troops by the end of this year. Whoever wins will inherit an impoverished country mired in insurgency and facing high unemployment and declining foreign aid.

Both candidates have promised to sign a security pact with the Obama administration that would allow nearly 10,000 American forces to remain in the country in a training capacity and to conduct counterterrorism operations. A disruption in the announcement of election results could mean another delay in finalizing that agreement, which was rebuffed by Karzai.

Abdullah Abdullah, who garnered the most votes in the first round of voting on April 5 but failed to get the majority needed to win outright, has boycotted the electoral institutions after alleging widespread ballot box stuffing and other efforts to rig the June 14 runoff vote against him. His rival Ashraf Ghani Ahmadzai. Ahmadzai, a former finance minister and World Bank official, also filed complaints of irregularities in the balloting but has insisted that the agreed-upon counting process be respected and said any further delays in releasing results would be unacceptable.

Preliminary results had been due on Wednesday, but the Independent Election Commission postponed them for five days saying it needed to audit votes from nearly 2,000 of 23,000 polling stations nationwide. Commission chairman Ahmad Yousuf Nouristani said Sunday that the announcement would be made Monday as planned, although a time had yet to be announced.

Abdullah said Sunday that he would not accept any results until all fraudulent votes were invalidated. He also demanded a more extensive investigation into suspicious ballots, including cases where more than 93 percent of the ballots in a single box were for a single candidate.

"What we are asking for is . an audit and after the completion of the audit before the announcement of the preliminary results should be made," he said Sunday at a news conference.

"There is no doubt that fraud has happened, massive fraud has happened," he said. "After all suspicious areas are audited, we will accept the election results, but not before that."

The European Union's election monitoring team in Kabul also has called for a broader investigation into fraud allegations, including highly improbable votes for a single candidate in polling stations or unlikely discrepancies between votes cast by women and men.

Diplomats and other international officials have long said they anticipated irregularities and the determining factor would be whether the vote rigging was sufficient to affect the overall outcome. The 2009 re-election of Karzai was marred by widespread ballot box stuffing and proxy voting, leading Abdullah, who was runner-up at the time, to refuse to participate in the runoff.

The Taliban threatened a campaign of violence to disrupting the Western-backed process, but millions of voters still went to the polls and the balloting was relatively smooth despite a series of high-profile attacks

According to the election commission's official timetable, final results on July 22. Karzai has set Aug. 2 as the date for the new president to be inaugurated.

Ahmadzai said more delays would be "unacceptable" and would "create serious doubts and mistrust of the people about the election process."

"The announcement of preliminary results cannot be postponed further," he said Saturday at a news conference.

Both campaign teams, meanwhile, were holding technical and political talks in a bid to resolve the crisis, although both candidates have ruled out a deal on a coalition government.

U.S. Sen. Carl Levin, who met with both candidates during a visit to Kabul, said he had been assured a consensus was emerging that would allow the release of partial results on Monday but also provide for a more comprehensive audit of contested votes before a final announcement is made.

"I am confident that they're going to agree on the details of that audit. Both want it. Both need it," the Michigan Democrat told reporters. Levin, the chairman of the Senate Armed Services Committee, warned that the level of continued aid from war-weary Americans was at stake.

"It is essential that these candidates find a process, agree on a process, live by a process that resolves this presidential race because if that falls apart then I think it's going to be very difficult to maintain the economic support," he said.