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Ruling party candidate Felipe Calderon built an insurmountable lead in Mexico's presidential vote count Thursday, but his leftist rival vowed to challenge the results in court.

With 99.92 percent of the vote counted, Felipe Calderon would win even if all the remaining votes went to Andres Manuel Lopez Obrador of the Democratic Revolution Party. He had 35.87 percent of the vote, compared with 35.32 percent for Lopez Obrador. Roughly 220,000 votes separated them.

Roberto Madrazo of the Institutional Revolutionary Party had 22.27 percent and two minor party candidates split the rest of the vote.

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Fewer than 200,000 votes out of more than 41 million cast separated the two leading candidates.

Lopez Obrador supporters wept in the streets, saying they wouldn't let him be robbed of victory. At a news conference, Lopez Obrador urged his supporters to gather this weekend in downtown Mexico City, stirring fears he would mobilize massive protests that could lead to violence.

"We are going to the Federal Electoral Tribunal with the same demand — that the votes be counted — because we cannot accept these results," he said. "We are always going to act in a responsible manner, but at the same time, we have to defend the citizens' will."

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Lopez Obrador had led throughout the official count until he was overtaken by Calderon with 97 percent of the vote tallies recorded early Thursday. Ruling party officials said Lopez Obrador had been ahead only because his supporters had been stalling the count with protests in Calderon's strongholds.

Once the count is complete, it can be disputed before the tribunal. A winner must be declared by Sept. 6.

Lopez Obrador demanded that electoral officials carry out a manual ballot-by-ballot count, instead of just tallying vote totals as they have been doing.

But Luis Carlos Ugalde, president of the Federal Electoral Institute, said that was not possible.

"Mexican law is very clear on when a ballot box can be opened: only when there are problems with the vote tallies, when the tally sheet has obviously been changed, or when the box has been tampered with," Ugalde said.

Mexico's peso strengthened against the dollar early Thursday after the official tally showed the business-friendly Calderon leading.

Before dawn, as the count switched to Calderon's favor, he called for the country to move beyond the bitter race.

"Starting today, let us help Mexico begin a new era of peace, of reconciliation," he told hundreds of cheering supporters at his campaign headquarters.

Electoral workers at 300 district headquarters across the country were adding up results in the official tally that began Wednesday. By law, they were required to work nonstop until they finished the count.

Calling the election "the most democratic and cleanest in the history of Mexico," Calderon asked his rival and all Mexicans to erase the bitter divisions that arose during the lengthy campaign, and focus "not on our differences, but on our similarities."

He also turned his remarks to the millions who did not vote for him, asking them "to give me a chance to win your confidence."

In an exclusive interview with The Associated Press on Wednesday, Calderon offered to include Lopez Obrador in his Cabinet — an effort to build a coalition government and avoid weeks of political impasse. But he said he did not believe his rival would accept, adding that the two men had not spoken to each other since the election.

Thursday's official count capped four days of debate over the election results.

When polls closed, citizens staffing the 130,488 polling places opened the ballot boxes and counted the votes, then sealed them into packages with their tallies attached and reported unofficial totals to the Federal Electoral Institute. The institute then posted preliminary results on its Web site.

The sealed packages were delivered to district headquarters, where election workers used the tallies to add up the official vote totals.

Once the results have been turned over to the seven-judge Federal Electoral Tribunal, it hears any complaints and can overturn elections.

Leonel Cota, president of Lopez Obrador's Democratic Revolution Party, said the party might challenge the results in international tribunals.

Lopez Obrador stoked fears that Mexico was returning to its fraudulent past, in which the former ruling party rigged elections in its favor for decades.

"They know very well that they don't have anything to celebrate," he said of Calderon's party. "It is all choreographed. There is no joy. They know very well what they did."