MEXICO CITY — Leftist candidate Andres Manuel Lopez Obrador said he will file a formal legal challenge this week to the vote count in Mexico's presidential election.
The electoral authority issued final results Friday showing that former ruling party candidate Enrique Pena Nieto won by a 6.6-percentage-point margin, almost exactly the same lead as a quick count gave him the night of the election.
The final count, which included a ballot-by-ballot recount at more than half of polling places, showed Pena Nieto getting 38.21 percent of votes in Sunday's election. Lopez Obrador got 31.59 percent.
Lopez Obrador said the court challenge will be based on the allegation that Pena Nieto's Institutional Revolutionary Party, or PRI, engaged in vote-buying that illegally tilted millions of votes. PRI officials deny the charge.
His supporters planned to take to the streets of Mexico City to protest the results.
''Rivers of illicitly obtained money were used to buy millions of votes,'' Lopez Obrador said. He said that the recount of ballots at over half of polling places had not been done as thoroughly as promised.
The final vote count must be certified in September by the Federal Electoral Tribunal.
The tribunal has declined to overturn previously contested elections, including a 2006 presidential vote that was far closer than Sunday's.
Accusations of vote-buying began surfacing in June, but sharpened early last week as thousands of people rushed to grocery stores on the outskirts of Mexico City to redeem prepaid gift cards worth about $7.50. Many said they got the cards from PRI supporters before Sunday's elections.
Lopez Obrador said millions of voters had received either pre-paid cards, cash, groceries, construction materials, or appliances.
Lopez Obrador led a street protest in 2006 to protest alleged fraud in the presidential elections of that year, which he narrowly lost to President Felipe Calderon.
But he said last week that his challenge of the results would be channeled through legal venues, like the electoral institute and courts.
''We have acted and we will continue to act in a responsible way, adhering to the legal procedure. Nobody can say we are violating the law,'' Lopez Obrador said.
Leonardo Valdes, the president of the Federal Electoral Institute, said he does not see grounds for overturning the results.
''I do not see any justification for rejecting the entirety of the election results,'' Valdes said. ''Rejecting the results would be like rejecting the effort of those 50 million voters.''
However, he said the institute, Mexico's chief electoral watchdog agency, had begun an investigation into the gift cards, and had requested that the PRI and the grocery store chain that had the cards supply data.
In an interview with the paper Excelsior, Calderon said ''electoral authorities have an obligation, of course, to give us an answer'' about the allegations, adding ''what we need, in any case, are legal and institutional reforms, so that this kind of accusations don't arise again.''
Giving away such gifts is not illegal under Mexican electoral law, as long as the expense is reported to electoral authorities.