U.N.-backed fraud investigators on Monday threw out nearly a third of President Hamid Karzai's votes from the August election, undercutting his claim of victory and stepping up the pressure for him to accept a runoff.
U.S. President Barack Obama's administration has been holding off on a decision to send more troops to Afghanistan until a credible government is installed in Kabul.
Both U.S. Secretary of State Hillary Rodham Clinton and U.N. Secretary General Ban Ki-moon signaled on Monday that a resolution was near.
Clinton said Karzai planned to announce his intentions on Tuesday, adding that she was "encouraged at the direction the situation is moving."
A spokeswoman for Ban said he spoke with Karzai and the Afghan leader assured him he will "fully respect" the constitutional process even if it means a runoff against his top challenger, former Foreign Minister Abdullah Abdullah.
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The findings by the Electoral Complaints Commission dropped Karzai's votes to 48 percent of the total, below the 50 percent threshold needed for him to avoid a runoff, according to calculations by independent election monitors.
Still, it was uncertain whether the Afghan-led Independent Election Commission, which is dominated by Karzai supporters, would accept the findings and announce a second round.
Their independence was put into question when CBS News correspondent Mandy Clark visited officials counting the vote last month.
The commission assured Clark they set aside thousands of questionable ballots. But, when CBS News looked inside the quarantine room, nothing was there.
Karzai campaign spokesman Waheed Omar said the Karzai camp was waiting for the election commission to formally certify the U.N.-backed panel's findings, thereby giving them the force of law. Although short of an unequivocal pledge to accept a run-off, the statement appeared to represent a step in that direction after days of outright rejection.
Karzai's camp had complained about the panel of three foreigners and two Afghans which conducted the fraud investigation, saying foreigners were unfairly influencing the outcome.
Last week Karzai aides suggested he might contest the findings, setting off a series of last-minute diplomatic efforts, including visits by U.S. Sen. John Kerry, a Democrat and chairman of the Senate Foreign Relations Committee, as well as telephone calls by Clinton and British Prime Minister Gordon Brown.
Karzai met again late Monday with Kerry and U.S. Ambassador Karl Eikenberry to discuss the standoff.
The two-month election crisis threatens to undermine the Obama administration's Afghan strategy at a time when public support for the eight-year war is declining in the U.S. and the Taliban-led insurgents are gaining strength. The White House says Obama will not decide whether to send thousands more U.S. troops to Afghanistan until the political crisis is resolved.
Preliminary results released last month showed Karzai winning more than 54 percent of the vote in the 36-candidate race. However, proclamation of a Karzai victory was withheld until the U.N.-backed commission finished its investigation into widespread fraud allegations.
The inquiry was concluded last week, but the panel withheld releasing the findings while talks were held with the Karzai-dominated election commission that must certify the results and order any runoff.
The U.N.-backed panel decided to release its report Monday after the Afghan commissioners kept insisting on changes that would show Karzai winning outright. The officials spoke on condition of anonymity because of the sensitivity of the issue.
Abdullah campaign spokesman Fazel Sancharaki welcomed the fraud panel's findings as "a step forward" and said the election commission had no choice but to call a runoff.
Afghans close to Karzai said the president feared the runoff was part of an Obama administration plan to oust him - a charge the U.S. has repeatedly denied. They spoke on condition of anonymity because they were not supposed to speak for Karzai.
Afghan officials say they can organize a runoff in about two weeks, which is close to the start of winter. After the first snows fall in the high mountain passes, it will become all but impossible to hold an election until the spring. A second round vote would also run the risk of Taliban attacks on voters similar to those carried out during the first ballot.
For those reasons, Western diplomats have urged the two sides to reach a power-sharing agreement which would avoid a new vote and bring an end to the crisis. Former U.S. Ambassador Zalmay Khalilzad and others held a series of weekend talks with the rival camps on a possible power-sharing deal.
Officials familiar with the talks, speaking on condition of anonymity because the discussions were confidential, said both sides were open to the power-sharing idea but were far apart on details. Karzai has said he would be willing to offer posts to the opposition in a new government - which falls short of a real coalition with clearly defined powers.
After the auditors' findings were released, U.N. spokesman Aleem Siddique said a runoff "isn't optional."
"It's a requirement of Afghan electoral law, and we expect the institutions of this country to follow the law to the letter," he said.
The U.S. Embassy called on the election commission "to implement these orders with all due speed."
Grant Kippen, the Canadian who heads the fraud panel, said he did not see any legal way for the election commission to reject the findings.
"Our decisions, our orders, are final and binding according to the law," Kippen said. "We've followed the law very clearly, very precisely. My sense is that the IEC is going to follow the law as well."
Investigators released only raw data from their findings, but it was clear that more than 900,000 of Karzai's 3 million votes were voided, along with about 191,500 ballots cast for Abdullah. More than 5 million votes were cast, of which 1.3 million invalidated, according to Democracy International, the election monitoring group that calculated Karzai's totals at 48 percent.
Karzai, who came to power soon after the collapse of the Taliban in the U.S.-led invasion of 2001, was close to the Bush administration but fell out of favor in Washington because of perceived weakness and indecision in the face of a growing insurgency which exploited Afghan public frustration over corrupt and ineffectual government.
Much of the electoral fraud appeared to have occurred in the south, homeland of Karzai's fellow ethnic Pashtuns where the Taliban are strongest. Taliban threats kept thousands of Pashtuns from the polls in areas where the president had been expected to run strong.