Ivory Coast
Thiam blamed 'judicial harrassment' for his decision to leave the presidency of the Democratic Party of Côte d'Ivoire (PDCI).
The PDCI was due to meet on Monday to name an interim leader.
Thiam's presidency was already the subject of a court challenge. A party activist petitioned court questioning the legality of his election as party leader in December 2023.
It is the latest roadblock the former banker has faced in his quest to become Ivory Coast's president.
Last month, a magistrate in Abidjan invoked the country's nationality law to order Thiam's removal from the voter's register, effectively ending his bid for the presidency.
Thiam held French citizenship before renouncing it to become Ivorian. In a video statement Sunday, Thiam said he was the target of a harrassment campaign.
He accused his attackers of instrumentalizing the judiciary.
00:58
Guinea Bissau: Military court returns main opposition leader to prison
01:50
Algeria counts votes in legislative poll marked by low turnout
00:58
Algerians vote for new parliament with turnout in focus
02:14
Burkina Faso: what will change after the diplomatic rupture with France?
01:05
Zimbabwean parliament approves extending presidential term by two years
01:53
Zimbabwean citizen recounts leaving South Africa over anti-migrant sentiment