Leaders of the Mexican left called Friday for a peaceful popular mobilization to annul the July 1 presidential election amid allegations of vote-buying and other machinations by the victorious Institutional Revolutionary Party, or PRI.

"We are asking that the presidential election be invalidated because there are very serious violations of the constitution," the leftist standard-bearer in the contest, Andres Manuel Lopez Obrador, said at a press conference in Mexico City.

"We will always act peacefully," he said at the presentation of the National Plan for Defense of Democracy and the Dignity of Mexico.

The PRI's Enrique Peña Nieto won the election with 38.21 percent of the vote, while Lopez Obrador took second place with 31.59 percent, according to the final official tally.

But the leftist hopeful filed a motion last week with the TEPJF electoral court seeking to have the election overturned, pointing to mounting evidence of irregularities.

The initiative announced Friday will begin next week with a coordinated message in the mass media and on social networks, to be followed July 29 by information assemblies in 142 city squares across Mexico.

The activities will continue until at least Sept. 6, the deadline for the TEPJF to certify Peña Nieto as president-elect, Lopez Obrador said.

The mobilization is "open to women, men of good will" who are not ready to give up the possibility of "a democratic republic" in Mexico, the former capital mayor said.

He said the mobilization will not include the disruptive street protests and occupations carried out by his supporters after he narrowly lost the 2006 presidential contest.

"Our adversaries want us to fall into the trap of provocation, of violence," Lopez Obrador said. "They will be disappointed. We don't want to give pretexts to the violent ones."

He urged the TEPJF and other authorities to "deepen the investigation" into the PRI's vote-buying and said that the left had received information from "many PRIistas who are horrified about what happened, who are repentant."

"It would be an injury of great magnitude to the people of Mexico to validate an election such as the one the PRI wants to buy to impose Peña Nieto," Lopez Obrador said.

Mexico's conservative governing party has joined the leftist coalition in demanding an investigation of the PRI's campaign finances.

The respective chairmen of the National Action Party and the leftist PRD, Gustavo Madero and Jesus Zambrano, held a joint press conference to announce their plans to file a formal complaint with the Attorney General's Office.

Zambrano said Madero was showing political courage by pressing for an examination of the PRI's financial activities.

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 Felipe Calderon by 0.56 percent of the vote, a result the leftist candidate refused to accept.

Mexico's non-partisan Yo soy 132 student movement is also mounting a campaign aimed at persuading authorities to annul the presidential election and avert the "imposition" of Peña Nieto as the country's next head of state.

"Our general plan begins by contributing to the cleaning up of the electoral process, but it has as its goal the legitimate petition to declare the election invalid," one of the group's representatives, Sofia Silva, said Thursday.

Yo soy 132 emerged in May, largely as a reaction to the Mexican mass media's bias in favor of Peña Nieto and the PRI.

The movement has already submitted to prosecutors and electoral authorities a report containing more than 1,000 instances of irregularities at polling places and said it will deliver a second dossier next week.

The movement's spokespeople announced a "national mega-march against the imposition," urging Mexicans to fill town squares across the country on Sunday. EFE