Two weeks after Costa Rica's election, there is still no decision on which candidate will be named president.
Otton Solis is now leading the presidential contest
With 80% of the votes manually recounted, centre-leftist Otton Solis is now leading with 41.4%, while Nobel laureate Oscar Arias has 40.1%.
After the initial count, former President Arias had a lead of less than 0.3% over his rival, one of the closest finishes in Costa Rica's history.
The Supreme Electoral Council has not said when the outcome will be released.
But it said it hoped to finish the manual recount by Wednesday.
There have been hundreds of allegations of irregularities, including complaints from Mr Solis' party, and the authorities are investigating them.
Neither candidate has claimed victory.
The front-runners go through to a second round if the winner does not get at least 40%.
Mr Arias, 65, had enjoyed a big lead over his rival in opinion polls.
But far from the easy victory that had been predicted for him, the election became the hardest-fought vote in the last four decades, with the two leading candidates virtually neck-and-neck.
Oscar Arias was expected to win outright
According to the original electronic count, Mr Arias, from the National Liberation Party, had 40.5%, compared with 40.2% for Mr Solis from the Citizens' Action Party - a difference of fewer than 3,300 votes.
The election comes amid wide disillusionment with politics after a string of corruption scandals in the country.
Three former presidents have been accused of taking illicit payments from foreign companies. Two of them are on trial.
Mr Arias is not among them, and many Costa Ricans see him as a politician untainted by the recent scandals.
But his critics describe him as arrogant.
Mr Arias - who was president between 1986 and 1990 - won the Nobel Peace Prize in 1987 for spearheading talks that led to the end of civil wars in Nicaragua and El Salvador.
He says he wants Costa Rica to join the Central American Free Trade Agreement (Cafta) with the US.
Costa Rica is the only country in the region which has not ratified the deal, which is set to come into effect later this year.
Mr Solis wants some of the deal to be renegotiated, arguing that in its current form it would exacerbate poverty and hurt small-scale farmers.
He is hoping to ride the left-wing wave sweeping through some Latin American countries.