Guinea's electoral body has called opposition leader Cellou Dalein Diallo's self-proclaimed victory in the first round of a presidential election "void". 

“Despite the serious anomalies that marred the smooth running of the … election and in view of the results that came out of the ballot boxes, I am victorious in this election in the first round,” Diallo told supporters on Monday, a day after the vote was held.

Diallo's supporters  chanted "Cellou, president". But elsewhere in the city, joyous celebrations by supporters devolved into clashes with security forces.

Diallo, 68, is the main challenger to Guinea’s 82-year-old incumbent President Alpha Conde, who is seeking a controversial third term after he pushed through constitutional reforms in March.  

The move sparked mass protests and subsequent crackdowns, which killed dozens of people. 

But Mamadi Kaba, a  spokesman of Guinea electoral commission said on Monday:  "I would therefore like to reassure the people of Guinea who voted yesterday in peace, without violence, that no provisional results have been proclaimed for the time being. 

"The Independent National Electoral Commission is the only institution empowered to proclaim provisional results."

Although Sunday, the day of the vote, was mostly calm, Diallo's self-proclaimed election victory has set the stage for a showdown with Conde.

The government insists the vote was fair and that the official electoral authority must declare the results.

Conde's RPG party said in a statement Monday that it condemned "with the utmost firmness the irresponsible and dangerous declaration" by Diallo.

 It called for its activists to remain calm.