A former Marxist rebel commander's tiny lead in El Salvador's presidential election is irreversible, the country's electoral tribunal said on Monday even as his right-wing challenger declared he was the real winner.
The dispute raises the prospect of legal challenges. However it is resolved, the victor will have a weak mandate to govern.
Salvador Sanchez Ceren of the ruling Farabundo Marti National Liberation Front (FMLN), which as a rebel group fought a string of US-backed governments in the 1980-92 civil war, claimed victory on Sunday after preliminary results showed he won 50.11 percent support.
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 claimed fraud and insisted he had won.
The two men were separated by just 6,634 votes.
"We put our technical teams to work all night, which is why I can tell you with certainty that the result of this election is irreversible," Eugenio Chicas, head of El Salvador's electoral tribunal, told reporters. He said definitive results would be ready in three or four days.
The FMLN and Arena — founded by the late Roberto D'Aubuisson, who had links to death squads — were fierce enemies during the civil war that killed about 75,000 people.
Quijano accused the election tribunal of corruption and hinted at foul play.
"We are not going to allow fraud ... We are 100 percent convinced that we have won," he said. "They are not going to steal this victory. We will fight, if necessary with our lives."
The election authority has not yet formally declared Sanchez Ceren the winner, saying it needs to review challenges to some ballots and was waiting for the final vote count.
Sanchez Ceren claimed victory after the preliminary results showed him winning and he promised to govern for workers and business leaders alike.
"We are going to govern for everyone, for those who voted for us, and those who did not," Sanchez Ceren told supporters.
Sanchez Ceren won 49 percent of the vote in the first round of voting last month, 10 percentage points more than Quijano and just shy of the majority needed to avoid a run-off. He had been the clear favorite to win heading into Sunday's vote.
The tight vote will force the eventual winner to tread a more moderate line, said Javier Oliva, a political scientist at the National Autonomous University of Mexico, particularly with congressional elections due in 2015.
"They will have to be more prudent," he said. "It could provide significant stability in institutional terms."
Quijano picked up support from moderate conservatives in the last month by portraying Sanchez Ceren as a communist with blood on his hands who would veer hard to the left and impose radical policies.
After initially campaigning on a proposal to use the army to fight street gangs, or maras, Quijano changed strategy after the first round and instead warned that Sanchez Ceren would follow the path of Venezuela's socialist government, which has taken over private businesses.
A carpenter's ninth son, Sanchez Ceren was a rural school teacher before joining the FMLN guerrilla movement and he then rose to lead one of its five main factions during the war.
Along with other FMLN leaders, he has moderated his policies since the peace accords were signed in 1992 and the rebel group became a political party.
If confirmed, Sanchez Ceren's victory gives the FMLN a second consecutive term. The affable, media-shy 69-year-old has said he will build on its social programs, which include a glass of milk a day for children and free school uniforms, shoes and supplies.
(Additional reporting by Noe Torres in San Salvador and Dave Graham, Miguel Gutierrez, Alexandra Alper and Julia Symmes Cobb; Writing by Simon Gardner; Editing by Kieran Murray and Ross Colvin)