French navy frogmen have found some 50 unexploded World War II shells off the southern port of Marseille, local authorities said Saturday.

The divers discovered the ordnance at a depth of 25 metres (709 feet), the maritime prefect's office said in a statement.

Specialist teams will defuse them in a four-day operation starting Monday, the statement added.

Bathing and diving have been banned within a 600-metre (yard) radius of the find during the operation.

The area has also been sealed off to vessels.