About 40 sailors on the Charles de Gaulle are under medical observation, it said in a statement, and those with symptoms have been placed in isolation.

None have shown signs of serious illness.

"As of today, a screening team with test means will be sent aboard the aircraft carrier to investigate the cases that have arisen and to hinder the spread of the virus on board the ship," the ministry said.

The ship, which can transport about 2,000 sailors, had been deployed in the Atlantic as part of a NATO exercise after having participated in Operation Chammal that seeks to contain the Islamic State group in Iraq and Syria. It was preparing for its return to the Mediterranean.

"It was decided to bring forward its return to Toulon, initially scheduled for 23 April," said the statement.

In the United States, Acting Navy Secretary Thomas Modly resigned Tuesday after mishandling a coronavirus outbreak on the USS Theodore Roosevelt aircraft carrier, Defense Secretary Mark Esper said.

Modly had removed the ship's captain, Brett Crozier, for writing a letter -- leaked to the media -- complaining of an uncontrolled virus outbreak among the Roosevelt's 4,800 crew and alleging the Pentagon was not paying adequate attention to it.

The Roosevelt has been docked for 11 days in Guam so the crew, with well over 100 confirmed coronavirus cases, can be tested and the vessel cleaned.