It is unclear whether his detention is linked to Sunday's foiled coup attempt by the army. Authorities have yet to release an official list of suspects.

Azannai condemned the coup attempt in a Facebook statement on Wednesday but also denounced attempts to "exploit the criminal events... for the purpose of seizing power through manipulation and intimidation of dissenting voices and critical political opinions".

The police source, who requested anonymity, gave no details on the reasons behind the arrest, nor the location where Azannai is being held.

A close associate confirmed the arrest, adding they had "no information" about the motive.

A key political figure and outspoken critic of President Patrice Talon, Azannai helped bring him to power in 2016 before breaking with him and joining the opposition.

Talon has been praised for Benin's economic development, but critics say he has become increasingly autocratic.

He is due to reach the end of his second term in 2026, the maximum allowed by the constitution.