* Capriles seeks to overturn vote in Supreme Court
* Political dispute destabilizes OPEC nation (Adds Capriles comments)
By Brian Ellsworth and Diego Ore
CARACAS, May 2 (Reuters) - Venezuelan opposition leader Henrique Capriles challenged President Nicolas Maduro's narrow election victory before the Supreme Court on Thursday, prolonging what appears to be a futile effort to overturn last month's vote.
Capriles refused to accept the results of the April 14 vote for a successor to late socialist leader Hugo Chavez, and called on supporters to take the streets. That led to unruly demonstrations in which the government says nine people died.
Few expect Capriles to win a favorable ruling from the court, which the opposition says is controlled by the ruling Socialist Party. He may also go to international tribunals, though most countries have recognized Maduro's win.
"This appeal seeks to annul the elections and request new presidential elections in Venezuela," said Gerardo Fernandez, a lawyer representing the opposition, who are intent on at least discrediting Maduro even if they cannot overrule the result.
"We've come to defend the citizens who voted in April 14."
Fernandez said the appeal includes complaints relating to incidents prior to the election. The opposition accuses Maduro of using state resources and government media for his campaign.
Capriles also alleges there were thousands of irregularities on voting day, ranging from intimidation of poll station volunteers to illegal campaigning by government supporters.
"This is not over. No one here can get tired or throw in the towel," Capriles told a news conference, adding that his team had found names of 200,000 dead people on the electoral register.
As on previous occasions, Capriles' news conference was interrupted on television after a few minutes by a government "cadena" broadcast that all local channels are obliged to show live.
Opposition supporters responded by banging pots-and-pans in some neighborhoods in a traditional form of protest in Venezuela and some other Latin American countries.
FRAGILE POST-CHAVEZ ERA
Maduro pillories Capriles daily as a sore loser and "bourgeois cry-baby." He accuses Capriles of fomenting post-vote violence, including killings of government supporters and attacks on government-run clinics.
Residents of one Caracas community affected by post-election violence told Reuters that two people were shot and killed by opposition sympathizers following a protest.
The government also attributed a third fatality in the La Limonera community to opposition violence, but locals said that man was a victim of common crime.
The election was triggered by the March 5 death of Chavez, whose charismatic leadership and oil-financed social largesse made him a hero to the poor but a pariah to critics who called him a dictator.
Though he was anointed as Chavez's successor, Maduro beat Capriles by only 1.5 percentage points in contrast to Chavez's 11 point victory over the same rival last year.
With a weaker vote mandate and without Chavez's innate charisma, Maduro seems to have less control over the disparate socialist coalition that his predecessor ruled with an iron hand.
The vote dispute led to a punch-up in Congress on Tuesday that put several opposition deputies in hospital. Video footage showed government allies repeatedly punching one deputy in the face, leaving him bloodied and bruised.
The deputies had raised a banner saying "Coup in Parliament" after the pro-government leadership of the legislature prevented them from speaking during the session unless they explicitly recognized Maduro as president.
The government responded with a broadcast, set to eerie, suspense-thriller music, showing opposition deputies waving arms and one throwing a chair.
Julio Borges, the opposition deputy who bore the most notable wounds from the fracas, called Maduro a "big liar" in a Twitter post. "I challenge you to show the Assembly's closed circuit video footage without editing anything," he said.
Maduro allies have in most cases said they regretted the violence, but blame the incident on provocation by opposition deputies interrupting the session with whistles and air horns.
The pugnacious Prisons Minister Iris Varela was less cautious. "They really deserved the beating that they got," she said, according to local media. (Additional reporting by Andrew Cawthorne; Editing by Andrew Cawthorne and David Brunnstrom)