French President Francois Hollande on Wednesday threatened to ban demonstrations the day after protests in Paris over labour reforms turned violent, leaving 40 people injured and landing 44 in police custody.

"At a time when France is hosting the Euro (football tournament), when it is faced with terrorism, demonstrations can no longer be authorised if property and people and public property cannot be safeguarded," Hollande's spokesman, Stephane Le Foll, told a cabinet meeting.