A panel of United Nations-appointed experts issued findings for the first time on Monday showing that the fraud was so pervasive that Mr. Karzai had not won the Aug. 20 election outright, according to foreign and Afghan officials in the capital, Kabul.
The findings are a defining moment for Mr. Karzai, who initially received 54 percent of the vote, and believes he is the rightful winner. They place him in direct conflict with his main backer, the United States, and threaten to pitch the country into a major constitutional crisis, should he decide to reject them altogether. . . .
The special audit committee, the Electoral Complaints Commission, invalidated nearly a third of all ballots cast for Mr. Karzai, according to a New York Times analysis of the preliminary data. More precisely, 28 percent of Mr. Karzai’s 3,093,000 votes were discarded due to fraud, the analysis showed.
The result pushed Mr. Karzai’s final vote total to about 49 percent, below the threshold needed to avoid a runoff. An independent analysis by an election monitoring group, Democracy International, gave Mr. Karzai about 48.3 percent, The Associated Press reported. A Western official familiar with the results had predicted that result earlier Monday.
The committee also threw out 18 percent of the votes of Abdullah Abdullah, a former foreign minister and Mr. Karzai’s top challenger, leaving him with 31 percent of the total vote, more than the 28 percent he had originally polled.
The data remains preliminary until it is officially accepted by the Independent Election Commission, which received the results from the audit committee on Monday.
Mr. Karzai’s campaign officials have complained about the work of the five-member international-Afghan panel that conducted the fraud analysis, saying that foreigners were unfairly influencing its outcome. And Mr. Karzai himself indicated this weekend that he might oppose the results, setting off a flurry of last-minute diplomacy by western officials.
If the Independent Election Commission, the Afghan body that will certify Monday’s results, accepts them as required under Afghan election law, Mr. Karzai has few options. A runoff with Mr. Abdullah, is constitutionally mandated to take place within two weeks. But Mr. Karzai could use his influence over the commission to reject the findings.
That would pitch Afghanistan into a constitutional crisis just as the Obama administration is trying to make a decision on whether to send more troops here to halt the Taliban’s advance in the country’s deepening war.
A spokeswoman for the American Embassy in Kabul, Caitlin Hayden, said Mr. Kerry, Democrat of Massachusetts, spent three days in Kabul over the weekend, then returned Monday to speak with Mr. Karzai, attempting to defuse a deepening political crisis.
“We call on the I.E.C. to implement these orders with all due speed and look forward to the final certified results,” Ms. Hayden said in an e-mail message.
It is unclear if the two candidates would actually go through with a runoff. The coming winter weather and increasing insecurity in the south of the country would make holding a second round difficult, and many foreign officials have suggested that the two candidates might strike a power-sharing deal, something both candidates have denied.
“I still believe in terms of where we are politically; that it’s unlikely to be a second round,” one Western official who asked to remain anonymous said.
The audit committee completely discarded the results of 210 ballot boxes due to fraud, the electoral complaints commission said in a news release. That reduced Mr. Karzai’s total by 41,000 votes. But the far larger number of his discarded votes — 874,000 — were thrown out based on a statistical sampling of the total body of suspect votes, which were divided into six categories, according to the Times analysis of that portion of the data, which was released in raw form.
Mr. Abdullah, for his part, lost 10,807 votes from the eliminated ballot boxes. An additional 185,000 votes were removed from his totals based on the statistical formula, the Times analysis showed.
The preliminary vote count of the Aug. 20 election had given Mr. Karzai over 54 percent of the vote and Mr. Abdullah 28 percent.
Demonstrations in support of Mr. Karzai took place in Kandahar, in southern Afghanistan and in Ghazni Province in the center of the country on Monday. About 3,000 people gathered in a market in the district of Spinbaldak, shouting, “We don’t want foreigners to interfere in our election,” a complaint frequently offered by his campaign.