Mexico's political left accused the federal government of hiding information about money laundering by the Institutional Revolutionary Party, or PRI, in the lead-up to the July 1 elections, and challenged presumed President-elect Enrique Peña Nieto to a debate on alleged irregularities in the process.

In a press conference Wednesday in this capital, the runner-up in the balloting, leftist Andres Manuel Lopez Obrador, said he and his supporters are providing ample evidence to the TEPJF electoral court to secure "the invalidation of the presidential election as clearly in violation of the constitution."

"We're talking about billions of pesos" of illicit origin directed to the PRI's campaign to buy at least five million votes, Lopez Obrador, the candidate of a coalition led by his Party of the Democratic Revolution, or PRD, said.

"The whole truth can be ascertained. If we're providing this evidence (of illegal activity), imagine what officials with the Finance Secretariat and (the CNBV banking regulator) would be able to find out, if they don't know already," Lopez Obrador said.

"In the federal government, they already know what this was about," Lopez Obrador said, adding that he doesn't know why President Felipe Calderon's conservative National Action Party, or PAN, administration does not "reveal what they know about the use of illicit funds for the benefit for Peña Nieto."

But "hiding information isn't going to work because we're very persistent and aren't going to give up," he said in comments aimed at federal government officials and TEPJF justices.

That tribunal has until Aug. 31 to issue a ruling on the challenge filed by Lopez Obrador's Progressive Movement coalition, either certifying Peña Nieto the winner or calling for a new vote.

According to the final official results released by the Federal Electoral Institute, or IFE, the PRI's Peña Nieto won the presidential election with 38.21 percent of the vote, while Lopez Obrador took second place with 31.59 percent, a difference of roughly 3.3 million ballots.

Regarding the PRI's accusations that Lopez Obrador's Progressive Movement coalition used grassroots organizations as "parallel structures" to evade campaign finance rules, the politician said he has always emerged unscathed when false charges have been leveled against him and invited Peña Nieto to debate the subject with proof in hand either this month or next.

"I invite Peña Nieto to discuss this matter before the media, to talk about what we have, about the money we have, our assets, how we acquired them and who bought votes and who didn't in the presidential election, with all the evidence (in hand)," Lopez Obrador said.

He suggested that meeting be held at the TEPJF headquarters before citizen observers, saying it "would be very healthy to clear up this matter" and that he has a lot of questions for Peña Nieto.

Lopez Obrador added that the accusations against him do not worry him, calling them an act of "leg-pulling" and a product of the PRI leadership's "desperation" and "nervousness."

"Scoundrels think everyone's a scoundrel," he said, reiterating that his coalition will not allow "a group of corrupt individuals to seize control of the country."

The PRI on Tuesday called on the IFE to investigate the Progressive Movement's campaign, accusing it of committing fraud to evade inquiries about the origin and destination of its funds, violating campaign spending limits and hiding its expenses.

Information obtained by the PRI "allows us to confirm the diversion of public funds to the campaign of Andres Manuel Lopez Obrador from government entities run by members of the Progressive Movement coalition," PRI chairman Pedro Joaquin Coldwell said.

Lopez Obrador said Wednesday that no legal trickery will be able to "justify the validity of the presidential election" and he invited citizens to attend assemblies that will be held Sunday in 142 public squares nationwide and "continue to provide evidence."

"We have testimonials, notarized proof in which citizens reveal what they were offered ... in exchange for voting for the PRI," he said in his first press conference of the week.

The politico said he will provide the electoral tribunal a list of 4,891 people who received Monex bank debit cards in Tabasco state. Peña Nieto alleges those cards were used by PRI operatives to drum up support for Peña Nieto in poor areas of the country.

He called on the TEPJF to order the "CNBV and the Finance Secretariat to demand a report from Monex on all the contracts for the distribution of cards signed by companies or front men for Peña Nieto and the PRI," estimating that some 260,000 debit cards were distributed that would have cost more than 1 billion pesos ($73.5 million).

"I have no doubt it's money laundering," the leftist leader said, adding he hopes "authorities clear this up."

The PAN, whose candidate, Josefina Vazquez Mota, finished a distant third in the presidential election, also has joined with Lopez Obrador in demanding an investigation of the PRI's finances.

The ruling party approached electoral authorities on June 14 with a request to freeze the PRI's accounts with Monex bank on suspicion of violations of campaign finance law.

That party, however, has said it is not challenging the election results.

The PRI, which governed Mexico from 1929 to 2000, lost the 2000 presidential election to National Action and finished third in 2006.

During its 71 years of largely unchallenged hegemony, the PRI relied mainly on patronage and control of organized labor and the mass media, though it was not above resorting to outright vote-rigging and even violence.

Despite their ideological differences, National Action and the PRD have a history of working together at the state and local levels to battle the PRI.

That relationship was put under strain when Lopez Obrador lost the 2006 contest to National Action's Calderon by 0.56 percent of the vote, a result the leftist candidate refused to accept. EFE