The main opposition candidate in the Honduran presidential election has said he will not accept the poll count despite earlier vowing to respect it.
Salvador Nasralla says the electoral court is manipulating results.
With 82% of the ballots counted, President Juan Orlando Hernández, who is seeking re-election, is leading the official count by a narrow margin.
Earlier, thousands of protesters marched in the capital, Tegucigalpa, accusing the authorities of fraud.
Mr Hernández was trailing five points behind Mr Nasralla in Sunday's vote until the electoral court stopped updating its website on Monday.
When the count resumed the following day, Mr Nasralla's clear lead began to dramatically disappear and by Wednesday Mr Hernández had edged ahead.
In response, Mr Nasralla called on his supporters to take to the streets in protest.
He then agreed to sign a document, along with Mr Hernández, vowing to respect the final result after every disputed vote had been scrutinised.
However Mr Nasralla later said the document he had signed with Mr Hernández had "no validity".
The US state department has urged the authorities in Honduras to review the election results quickly.
Riot police watched over the protests in Honduras's capital, Tegucigalpa
The opposition, and international observers, have been suspicious of the slow pace of counting in a country of fewer than 10 million people.
But the authorities said votes from remote rural areas took relatively long to arrive at the counting centre.
Mr Hernández said he was sure the votes from rural areas would be for him, a factor in why both candidates claimed victory the day after the election.
On Tuesday evening Mr Nasralla asked his supporters to come out and protest on his behalf in Tegucigalpa, the country's capital city.
"We've already won the election," he said. "I'm not going to tolerate this and there are no reliable institutions in Honduras to defend us."
- 64-year-old former TV presenter and sports journalist
- Heads the Opposition Alliance Against the Dictatorship, a coalition of parties from the left and the right
- His parents are of Lebanese descent
- Ran for the presidency in 2013 but lost to Juan Orlando Hernández
- Has campaigned on a promise to battle corruption
Juan Orlando Hernández
- 49-year-old lawyer
- Heads the right-wing National Alliance
- Is the 15th of 17 children, two of his siblings are also in politics
- Is the first Honduran president to run for a second term after the supreme court lifted a ban on re-election
- Says that if elected, he will continue fighting Honduras' influential criminal gangs