Receive Breaking News updates as they occur
By Nelson Renteria and Michael O'Boyle SAN SALVADOR (Reuters) - A former Marxist guerrilla leader claimed victory in El Salvador's presidential election on Sunday as results showed him with a very thin lead but his conservative rival warned of fraud and insisted he was the winner. Salvador Sanchez Ceren of the ruling Farabundo Marti National Liberation Front (FMLN), which fought a series of U.S.-backed governments in a 1980-1992 civil war, had 50.11 percent of the vote with returns in from 99.95 percent of polling stations. His right-wing challenger Norman Quijano, a former mayor of San Salvador, had 49.89 percent in the run-off vote, which was called after Sanchez Ceren fell just short of a first-round victory last month. "We won the first round, and now we have won again in the second," Sanchez Ceren told supporters late on Sunday night.