Ex-Ivory Coast Prime Minister Guillaume Soro has questioned the legitimacy of elections scheduled for next month after he was barred from running for president.
Mr Soro, who is in exile in France, was excluded from the list of candidates approved by the constitutional court because he has a criminal conviction.
He wanted to challenge his former ally President Alassane Ouattara, who is running for a third term after his preferred successor died in July.
Talking to journalists in the French capital, Paris, Mr Soro said that the president had carried out a “civilian coup d’etat”.
He said he wanted to stop Mr Ouattara in his “mad venture by all legal and legitimate means”.
Former President Laurent Gbagbo has also been barred from running.
Protests over Mr Ouattara’s candidacy has led to the deaths of at least 12 people as demonstrators have clashed with police, the Reuters news agency reports.