Leftist presidential hopeful Andres Manuel Lopez Obrador filed a criminal complaint against top Mexican election officials, his latest challenge to the July 2 vote he apparently lost by a hair to the conservative candidate Felipe Calderon.

The complaint, filed with the Federal Attorney General's Office on Tuesday, argues that nine senior officials failed to stop business groups from funding advertisements against the leftist.

The ads, which portrayed the leftist as a "danger to Mexico" and compared him to Venezuelan President Hugo Chavez, broke electoral regulations, said Lopez Obrador aide Horacio Duarte who handed in the complaint.

"They sowed fear in the citizens about the option that (Lopez Obrador) represents," Duarte said.

Duarte argues that by failing to stop the adverts, the officials committed electoral crimes punishable by up to six years in prison. Federal prosecutors will examine the complaint and decide if they will file criminal charges.

Calderon, who says the vote was clean, has offered to meet with Lopez Obrador — a gesture the leftist rejected.

"Our hand is extended, the possibility of a personal meeting is still in the works," Calderon aide Cesar Nava said Tuesday in an interview with radio station Radio W.

Also Tuesday, Calderon met with teachers union boss Elba Esther Gordillo, one of Mexico's most powerful female politicians, in his latest step to assume the role of president-elect following an election he says was clean.

Gordillo addressed Calderon as the "president-elect of Mexico" in front of union delegates, even though the top election court has not declared a winner.

Lopez Obrador has already challenged the vote result with the Federal Electoral Tribunal, asking that all 41 million ballots are recounted. In the official count, Calderon won by just 0.6.

The leftist has convened street rallies calling for a recount, filling the capital's central plaza with hundreds of thousands of followers.

He has also called on artists, entertainers and intellectuals to join a campaign of peaceful, "civil resistance."

Actress Maria Rojo and other members of Lopez Obrador's Democratic Revolution Party joined a series of rotating, 24-hour fasts outside the electoral tribunal offices.

Lopez Obrador claims that a vote-by-vote recount is necessary for the legitimacy of any eventual successor to President Vincente Fox. He said the recount could be carried out in six days, something Calderon aides have called ridiculous.

The tribunal has until Aug. 31 to rule on the challenges and until Sep. 6 to name a new president.

Fox, of Calderon's National Action Party, leaves office on Dec.1. Mexican presidents are limited to one, six-year term.