Guinea's opposition coalition demanded the annulment of last week's parliamentary election on Friday, citing what it said were widespread irregularities in the voting process and threatening to call for protests.
The opposition's decision raised fears of a return to the political violence in which at least 50 people were killed in the months preceding the polls. The climate of instability has deterred mining investment in the world's largest bauxite exporter.
"The opposition demands the annulment of this election because of the scale of fraud witnessed," said a statement read by opposition spokesman Aboubacar Sylla during a news conference.
Sylla said the opposition reserved the right to use all legal means of protest, including public demonstrations across the West African country.
The opposition, which has accused the government of trying to rig voting lists, had warned it would not tolerate any attempt to steal the ballot.
A spokesman for President Alpha Conde's ruling RPG party called the decision "incomprehensible."
"The transparency of this vote was assured by the presence of international observers," Moustapha Naite said.
A European Union observer mission said on Monday that the weekend election was marred by serious organisation problems, including a failure to tackle problems with the voter lists, and called for the national electoral commission, CENI, to publish results bureau by bureau to ensure transparency.
CENI began gradually releasing election results on Wednesday with Conde's RPG party taking an early lead in several districts. The opposition rejected the results and pulled its delegates out of the national electoral commission on Thursday.
However, results published late on Friday after the opposition's announcement showed its UFDG and UFR parties won in the communes of Dixinn and Matam, two of the five voting areas which make up the capital, Conakry.