Karoui and his brother, Ghazi Karoui, have been under investigation since 2017 after anti-corruption watchdog I-Watch submitted a dossier accusing him of tax fraud, said Sofiene Sliti, spokesman for the judiciary department for financial cases.

"After an inquiry into the complaint filed by I-Watch and having summoned and heard the two men... the judge decided 10 days ago to charge Nabil Karoui and Ghazi Karoui with money laundering," he told AFP.

The judge also decided to freeze their assets and ban them from travelling abroad, Sliti said, ruling out any political motives for the rulings.

But Nabil Karoui's recently-formed political party, Heart of Tunisia, condemned the decision as a "vain attempt to damage the party and its president and to question his growing popularity".

The brothers in 2002 launched Karoui & Karoui, an international media and advertising company.

Nabil Karoui was an active supporter of President Beji Caid Essebsi's election in 2014 but has become a fierce opponent of Prime Minister Youssef Chahed.

In May, Karoui, who has also founded a major private television channel, Nessma, said he would run for the presidency in November polls to succeed Essebsi.