Bolivian President Evo Morales on Thursday vowed to accept official election results to be announced by the Supreme Electoral Tribunal (TSE) later this week.

The outcome of Sunday's general elections could show Morales, who is running for reelection, winning sufficient votes to be declared the winner, or that he has to face his closest rival in a runoff in December.

To win in the first round, Bolivian law requires a candidate to get more than 50 percent of votes or more than 40 percent with a 10-percent lead over his or her closest rival.

"We are going to respect the official results, whether it is the first round or a runoff," Morales told reporters at a press conference.

He added that a runoff would be "nice," because it would give him the chance to defeat all of the opposition groups, as they would likely unite behind a single candidate in a bid to beat the incumbent.

Preliminary results based on 83 percent of the ballots indicated Morales, of the Movement Towards Socialism (MAS), garnered a little over 45 percent of the votes compared to 38 percent for runner-up and ex-president Carlos Mesa, of the conservative Citizen Community party, leading to a runoff.

Mesa and his supporters have taken to the streets to press for a second round, despite the fact that the ballots have yet to be counted in full.

Meanwhile, election observers from the Washington-based Organization of American States (OAS) entered the fray by proposing that a second round be held to dispel any doubts.

"I don't agree with the (OAS observer) mission. They can't issue a recommendation before the official count has been completed. I am calling on international organizations to respect our Constitution," said the president.