The opposition candidate in Sunday's presidential poll in Nicaragua has rejected the victory of the incumbent President, Daniel Ortega.
Fabio Gadea said he could not accept the results presented by the electoral council because "they did not reflect the people's wishes".
With 85.8% of the ballots counted, the electoral authorities announced that Daniel Ortega had won with 62.65% of the votes.
They said Mr Gadea got 31% of the vote.
After announcing the latest figures, president of the Electoral Council Roberto Rivas congratulated Daniel Ortega, because "the trends shown by the results could not be reversed".
Mr Gadea of the Liberal Independent Party (PLI) said he had "well-founded suspicions that a fraud of an unprecedented nature and proportions" had taken place.
PLI representatives said their parallel counting suggested an even race "before taking into account the rural vote", where they believe Mr Gadea will perform well.
Several independent electoral observers who were not accredited by the Nicaraguan authorities pointed to reports of fraud.
Official observers have so far not detailed any significant problems.
The head of the mission from the Organisation of American States, Dante Caputo, said that his team had not seen "significant irregularities", but he called on the authorities to investigate all complaints.
Head of the European Union mission Luis Yanez said the polls had taken place "in a climate of normality and tranquillity".
Mr Ortega's candidacy was controversial as it was in breach of a ban on serving consecutive terms in the top office.
He was allowed to run after the Sandinista-controlled Supreme Court overturned the ban.
His supporters took to the streets to celebrate the election results.
"This is the victory of Christianity, socialism and solidarity," said Mr Ortega's wife and spokeswoman, Rosario Murillo.
Daniel Ortega has been a leading figure in Nicaraguan politics since he led the Sandinista movement to overthrew dictator Anastasio Somoza in 1979.
He ruled Nicaragua for the next 11 years - fighting a civil war against the US-backed Contra rebels - before being voted out of power in 1990.
He failed in successive bids for re-election in 1996 and 2001, but in 2006 he was voted back into office thanks to a much softer image and a divided opposition.
Many Nicaraguans have benefited from the social programmes set up by Mr Ortega's government in the last five years with financial help from his ally, Venezuelan President Hugo Chavez.
Voters were also electing members of the National Assembly, with reports indicating that the Sandinistas (FSLN) were on course to win a majority.