One of France's most powerful businessmen, Vincent Bollore, was detained for questioning in an investigation into alleged corruption during lucrative port deals in Africa.
Bollore's company denied wrongdoing, but its shares plunged about 8 percent on the unexpected detention. The Bollore Group has vast holdings from transport to media and the oil business, and 80,000 employees worldwide.
Bollore, 66, was taken into custody in the Paris suburb of Nanterre, along with other executives of his Bollore Group, according to a judicial official. The official spoke only on condition of anonymity to discuss an ongoing investigation.
In a statement, Bollore Group said its executives "welcome this opportunity to fully cooperate with the judicial authorities to restore the truth." It argued that the case is based on "a great misunderstanding of this economic sector and economic activity in general."
The investigation focuses on suspicions around port deals in 2009 and 2010 in Lome, the capital of the West African nation of Togo, and Conakry in Guinea.
Bollore Group is suspected of using its communications arm, Havas, to provide cut-rate services to African leaders, who then ensured that another subsidiary would win shipping terminal contracts.
Bollore Group said the logistics subsidiary, SVC Africa, "did not engage in any illegal actions" and that Havas provided its services "in full transparency." Bollore Group said it won the port contracts because of its long experience in Africa and 2 billion euros in investment on the continent in recent years.
Bollore-related companies have faced other legal cases in the past.
The tycoon is involved in many high-profile projects in France, such as the shared electric Autolib cars on the streets of Paris.
He is notably known for hosting friend Nicolas Sarkozy on his yacht days after Sarkozy was elected French president in 2007, raising concerns that Bollore would gain political favours in return.
In Guinea, the government did not immediately comment on the case.
Bollore has dominated operations at the container terminal in Guinea's capital since Conde became president in 2010, and the company has invested heavily in expanding the terminal. President Conde presided over the official launch of the extension work.
Havas worked on Conde's 2010 and 2015 campaigns, notably spearheading an operation to call voters with a recorded voice message from Conde that impressed many Guineans.
Le Monde quoted Guinean President Alpha Conde as saying in 2016: "Bollore fulfilled all the conditions of the bids. He's a friend, I favor friends. So what?"