Former Credit Suisse chief Tidjane Thiam and former President Laurent Gbagbo are barred from contesting next month's presidential election in the Ivory Coast, although Gbagbo's ex-wife, Simone Gbagbo, will be able to run, an official said on Monday.

President Alassane Ouattara, 83, announced in July that he would seek a fourth term in the world's top cocoa-producing nation, and analysts expect him to win, given the weak field of challengers.

But tensions over candidates' eligibility risk are fuelling unrest in Francophone West Africa's largest economy, which has a long history of election-related violence. Ouattara's government has promised a peaceful vote.

Thiam, the designated candidate of the main opposition party PDCI, was widely expected to be excluded after a court ruled in April that he should be removed from the electoral roll because he was a French national when he registered.

Ivory Coast law states that candidates must be Ivorian citizens and cannot hold another nationality.

Monday's decision, announced by Constitutional Council President Chantal Nanaba Camara, validated five candidacies out of 60, including Ouattara's. It came just over a month before the official campaign period begins on October 10.

Laurent Gbagbo's refusal to accept defeat in the 2010 election triggered a brief civil war that killed more than 3,000 people and only ended with his arrest alongside Simone Gbagbo at their Abidjan residence.

Laurent Gbagbo was tried and acquitted of crimes against humanity at the International Criminal Court.

Simone Gbagbo was convicted in an Ivorian court of offences against the state during the 2011 civil war, but Ouattara granted her amnesty in 2018.

Thiam said in a statement on Monday that the election next month risked becoming a "coronation" for Ouattara.

The former CEO of Credit Suisse also said a fourth term for Ouattara would be unconstitutional, though Ouattara has argued that a new constitution approved in 2016 reset his two-term limit.