French billionaire Vincent Bollore has been detained for questioning in an investigation into alleged corruption during lucrative port deals in Africa.
Mr Bollore was taken into custody on Tuesday in the Paris suburb of Nanterre, along with other employees of his Bollore Group, a judicial official said.
The company's shares fell on the news.
French newspaper Le Monde said the investigation focuses on suspicions around port deals in 2010 in Lome, the capital of the West African nation of Togo, and Conakry in Guinea.
The company is suspected of using communications and advertising subsidiary Havas to support African leaders who, it is claimed, then ensured that another subsidiary, Bollore Africa Logistics, would win shipping terminal contracts.