SAN SALVADOR (AFP) ― The parties of both candidates in El Salvador’s surprisingly tight presidential runoff clash claimed victory late Sunday.

Pre-election polls indicated that former guerrilla leader Salvador Sanchez Ceren of the Farabundo Marti National Liberation Front would easily defeat Norman Quijano with the conservative ARENA party. But with all of the returns tallied, the leftist candidate was leading by a tiny margin: 50.11 percent to 49.98, electoral authorities reported.

“We won the first round and now we have triumphed again in the runoff,” Sanchez Ceren told enthusiastic supporters amid an explosion of fireworks.

But his ARENA counterpart was convinced its side had won.

Quijano claimed victory in a speech to supporters, and insisted that he would not allow “fraud of the Chavista or (Nicolas) Maduro style like in Venezuela.”

He claimed that El Salvador’s military was “aware of the fraud that is being perpetrated” by election authorities along with the FMLN.

Sanchez Ceren had conciliatory words for his rival.

“We can say right now that you have the doors open to work with us to move El Salvador forward,” he said.

Election officials, likely expecting that vote results will be challenged and there will be calls for a recount, urged both sides to wait for final results.

“This tribunal recommends and orders that no party declare itself winner given such close results,” said Supreme Electoral Tribunal president Eugenio Chicas in a TV and radio message.

Sanchez Ceren, 69, is El Salvador‘s vice president. A former teacher and ex-education minister, he was one of five top guerrilla commanders during El Salvador’s bitter 1979-92 civil war, which pitted the FMLN against the U.S.-backed conservative government.

Conservatives were in power for two decades until 2009, when Salvadorans elected FMLN candidate Mauricio Funes, a former journalist, as their first leftist president.

The FMLN fell just shy of an outright victory in a first round vote last month, and Sanchez Ceren was expected to easily win the run-off vote.

Meanwhile Quijano, 67, the mayor of the capital city San Salvador, is a law and order candidate who campaigned on the country’s high crime rate and the notorious “mara” street gangs behind much of El Salvador’s drug dealing and extortion.

After the first-round vote, Quijano overhauled his image and talked more about keeping children out of gangs and rehabilitating those already ensnared by them.

Quijano however suffered from his links to ex-president Francisco Flores, a former campaign adviser, under scrutiny over $10 million donated by Taiwan that went missing during his 1999-2004 government.

ARENA removed Flores from his advisory job, but the controversy has damaged Quijano.