Planned attacks on sporting events, schools and religious sites on the French Riviera have been foiled since the killings of 86 people on Nice's seaside promenade in July, the city's prosecutor says.
"Several cases have been passed on to the anti-terrorism prosecutor in Paris," Prosecutor Jean-Michel Pretre told France 3 television.
"It was about religious sites, during certain celebrations, sporting events, stadiums, schools,"
The cases concern "people who started to articulate things that are rather precise about a type of target or even a specific target", the prosecutor is quoted as saying.
France is on high alert after a string of militant attacks over the last two years.
A Tunisian man drove a 19-tonne truck along a packed Nice promenade, mowing down people in the Bastille Day crowd on July 14, before he was shot dead by police.
Emergency rule has been in place since attacks on Paris in November last year in which Islamist militants killed 130 people.
Another 17 people were killed in January 2015 in attacks that began with the shooting of journalists working for Charlie Hebdo, a satirical weekly that had published cartoons mocking Islam.