But Subcommandante Marcos - who said in January that he now wanted to be known as Delegate Zero - also accused the mayor of Mexico City of betraying leftist principles supported by the Zapatistas, the land-rights movement that Marcos leads.
He said he wanted nothing to do with the election. "We are against all of the political class," Marcos said on the nation's main morning television news programme on Tuesday.
He said the election could be stained with blood if there was no solution to the long-running dispute between locals and police in San Salvador Atenco, on the outskirts of Mexico City, which recently exploded over the eviction of unlicensed flower vendors.
"These elections will have to be held with the army and police on the streets," Marcos, smoking his pipe, said during the hour-long interview on the Televisa network .
The rebel leader left his jungle hideout in January and is touring the country trying to forge a national leftist movement. The low-profile tour drew little interest until the trouble broke out in San Salvador Atenco last week.
He appeared to defend the actions of protesters against police, saying: "They were not beating the person, but rather what he represents."
News footage had shown farmers using petrol bombs against police, some of whom were badly beaten. But police also used violence against those that they arrested in the clash, and may have sexually abused some of them.
Marcos accused the establishment of provocation and said: "They are generating a scenario of violence that is going to escalate."
Marcos smoked his trusty pipe
during the hour-long interview
He compared the current climate with the social tension that led to the Zapatistas' brief armed uprising in January 1994 in the southern state of Chiapas - but he said that his group is now committed to peace.
He called the three main presidential contenders "mediocre", and said they offer no solutions to Mexico's serious problems.
"They are fighting for business and not for the direction of the country," he said.
With drug killings on the rise, strike battles and the San Salvador Atenco incident - the candidates must convince Mexicans that they can preserve law and order.
"We reject violence, and we reject repression," Gerardo Fernandez, spokesman for Lopez Obrador's Democratic Revolution Party, the PRD, said, in apparent reference to reports of police abuse of detainees in last week's clash.
"It's a lie, that they [rival parties] ... are trying to associate us with instability and violence," he said.
Lopez Obrador's support is falling
Lopez Obrador led blockades of oil wells in the 1990s to demand damage payments for farmers, but the PRD is now trying to strike a middle road, between the government's get-tough approach and the party's traditional leftist base.
Recent polls show Felipe Calderon of the conservative National Action Party of Vicente Fox, the current president, taking the lead from Lopez Obrador.
Marcos said that if Lopez Obrador was elected, he would have an "administration of handouts", while Calderon would mean more of the same disappointing policies the country has had under Fox, who took office in 2000.
But the worst of all three candidates, he said, was Roberto Madrazo, of the Institutional Revolutionary Party.
"No one trusts him, not even his family," said Marcos, who was identified by Mexican authorities in 1995 as Rafael Sebastian Guillen, a former university lecturer.
Zapatista Army of National Liberation (EZLN)