Guinea's opposition is calling for a re-run of Sunday's presidential election even before the votes have been counted.
It alleged widespread fraud, including ballot boxes being stuffed and some 400 polling stations staying closed.
This is the country's second democratic presidential election since it gained independence from France in 1958.
Several people were killed in clashes during the election campaign.
The main opposition leader, Cellou Dalein Diallo, said they will not accept the results, they will not give in and that they will protest.
He was speaking at a press conference attended by the six other candidates challenging incumbent President Alpha Conde, who was standing for a second term.
Mr Conde became president in 2010 in the country's first democratic election after decades of fighting authoritarian regimes, during which he was sent into exile and prison.
He defeated Mr Diallo in a run-off.
The electoral commission says the results won't be announced until the end of this week.