The Mexican left shifted its effort to dig up evidence of irregularities in this month's presidential election into high gear over the weekend with the backing of supporters who have set up nearly 150 people's assemblies.

"These assemblies have the purpose of informing all citizens about what we are doing to get the Electoral Tribunal to invalidate the presidential election," leftist presidential candidate Andres Manuel Lopez Obrador told the gathering Sunday in Nezahualcóytl, a city in Mexico state.

Institutional Revolutionary Party, or PRI, candidate Enrique Peña Nieto won the presidential election with 38.21 percent of the vote, while Lopez Obrador took second place with 31.59 percent, according to the final official results released by the Federal Electoral Institute, or IFE.

The leftist politician, who was accompanied by his wife, Beatriz Gutierrez, urged his supporters to work hard to document the election irregularities.

"This effort is not in vain, the sacrifices we are making. If we surrender, then, yes, a dictatorial regime will be fully established and we will become slaves in our own land. And that will never happen. We are always going to stand tall, fighting for dignity and for justice," Lopez Obrador said.

The former presidential candidate, who was the candidate of the leftist Progressive Movement, criticized those who ripped him last week for calling for an "interim presidency," arguing that he did not intend to "destabilize the country."

"We are going to continue this fight in defense of democracy, of the dignity of Mexico, because if we cross our arms then the elections fraud, the imposition, will be consummated, and nothing good would come of that for Mexicans," Lopez Obrador said.

"Fighting for the constitution and democracy is to give stability to our country. Let there be peace, let there be calm in Mexico!" the leftist politician said.

Lopez Obrador's supporters gathered in plazas across Mexico on Sunday to draw attention to the alleged irregularities.

The politician, who was the candidate of a coalition of leftist parties led by the Party of the Democratic Revolution, or PRD, plans to hold an "Expofraude" on Aug. 12 at which evidence of election irregularities will be presented to the public.

The PRD and the conservative National Action Party, or PAN, announced earlier this month that they planned to jointly file a complaint with the Attorney General's Office on alleged money laundering by the PRI.

The two parties also filed a request with the IFE for a speedy investigation of allegations of irregular use of campaign funds by the PRI, which governed Mexico from 1929 to 2000.

The TEPJF electoral court 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. EFE