Venezuelan opposition leader Henrique Capriles has launched a formal legal challenge disputing the results of last month's presidential poll.
The centre-right politician submitted on Thursday his appeal to the Supreme Court, even though opposition has said the tribunal is loaded with judges supporting late President Hugo Chavez and is certain to reject the challenge.
The court has 72 days to respond to the appeal to annul the election results.
Ramon Jose Medina, an opposition coalition official, said the complaint alleged "bribery, violence and fraud" throughout the electoral process that ended in victory for Chavez's hand-picked successor, Nicolas Maduro, over Capriles.
Capriles, 40, said he faced a difficult path through the country's top court but he was willing to take the case to the international community.
"We are going to exhaust all the internal institutions because we have no doubt that this case will end up in the international community," he said.
Capriles, a state governor, had been under a Monday deadline if he wanted to file with the top court.
Tensions have soared since the April 14 vote, after which official results gave victory to Maduro by a narrow 1.5 percent margin.
Capriles had lost to Chavez himself last October by 11 points.
Capriles has accused Maduro of stealing the election and rejected an audit of the vote by the National Electoral Council, which began on Monday, as a farce, after it refused to look at physical voting records.
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The council has limited itself to a narrow, technical review of the electronic voting system and said that no audit could reverse Maduro's win.
Maduro led a May Day march in central and western Caracas, and made a last-minute route change to avoid a confrontation with opposition marchers, who chose a major road in the east of the capital for their demonstration.
Addressing supporters on Wednesday with all the gusto and populist rhetoric of Chavez, Maduro accused the "cry-baby" Capriles and his opposition of a fascist agenda bent on bringing the bourgeoisie to power.
"There is a small group of right-wing fascists who have hijacked the Venezuelan opposition and are leading the fascist project, the ultra-right, the extremists, from the old bourgeoisie, the masters of the valley," he told thousands of supporters in Plaza O'Leary, in a speech carried on national television.
"Accept your defeat fascist! Stop with the kicking, the whining. You are a whiny, bourgeois fascist who wants to incite hatred and violence in the country."
Wednesday's marches came a day after a brawl broke out in the National Assembly over the pro-Chavez majority's refusal to grant the opposition the right to speak until they recognised Maduro as the winner of the election.
Videos issued by opposition deputies showed the politicians coming to blows.