* Leftist ex-rebel leads by 6,364 votes in final recount
* Right-wing challenger files to annul election
* May take days to process legal challenge - tribunal
SAN SALVADOR, March 13 (Reuters) - A former Marxist guerrilla leader held a narrow lead in El Salvador’s presidential election, final results showed on Thursday, but officials held back from declaring him the winner as his right-wing rival wants the vote annulled.
Salvador Sanchez Ceren of the ruling Farabundo Marti National Liberation Front (FMLN), which as a militant group fought a string of U.S.-backed governments in the 1980-92 civil war, won 50.11 percent support in Sunday’s vote, results showed.
Challenger Norman Quijano, the 67-year-old former mayor of San Salvador and candidate of the right-wing Nationalist Republican Alliance (Arena) party, had 49.89 percent support. He has filed a claim to annul the election due to fraud.
Electoral tribunal president Eugenio Chicas said the five-member court unanimously validated the election results. Sanchez Ceren’s beat Quijano by 6,364 votes.
The tribunal says it may take until Sunday or Monday to work through Quijano’s legal challenge to the election.
Quijano claimed on Wednesday to have proof that 20,000 people had voted twice, but refused to share proof with media. International observers said they had seen no evidence of widespread fraud.
Sanchez Ceren, who would be the first ex-rebel to become president if he takes over from incumbent Mauricio Funes, has promised to make a “national pact” with conservative parties and business owners, and to establish a moderate government.
Quijano has tried to paint him as a radical in disguise who would bow to the influence of socialist Venezuela.