Venezuela’s acting President Nicolas Maduro was declared the winner of the election to succeed late President Hugo Chavez by a razor-thin margin late Sunday, but his rival refused to concede defeat.

Venezuela's acting President Nicolas Maduro was declared the winner of the election to succeed late President Hugo Chavez by a razor-thin margin late Sunday, but his rival refused to concede defeat.

Fireworks erupted after the National Electoral Council announced that the "irreversible" results showed Maduro had won with 50.66 percent of the vote compared to 49.1 percent for Capriles -- a difference of less than 300,000 votes.

"Mission accomplished Commandant Chavez. The people fulfilled its pledge," Maduro said in front of cheering supporters at the Miraflores presidential palace.

The 50-year-old former foreign minister declared that he secured a "fair, legal, constitutional" victory. But he said he was open to an audit of the close vote tally.

He is scheduled to be sworn-in to complete Chavez's six-year term on Friday.

Maduro said he spoke with Capriles by telephone and that he told his rival he must recognize the outcome of the election. Both candidates had pledged during the campaign to accept the results.

But Capriles -- who had accepted defeat when Chavez beat him by 11 points in October polls refuted Sunday’s results.

"Today's loser is you," he told a news conference, referring to Maduro, adding: "We won't recognize a result until every vote has been counted."

The 40-year-old state governor demanded a recount of the backup paper ballots that are printed out by the electronic voting machines.

Hours earlier, Capriles claimed that there were attempts to let people vote after polling stations closed. He also accused the government of pressuring civil servants to vote for Maduro.

However, the National Electoral Council president Tibisay Lucena said the results were "irreversible" after 99 percent of electronic votes were counted, with 78.7 percent turnout.