A government official told The Associated Press that authorities have counted about 15 drone flights over a half-dozen nuclear sites since October 1.
Authorities insist France's nuclear facilities are designed to handle seismic and security risks, including those possibly posed by drones.
Environment Minister Segolene Royal told various media yesterday that investigators have no leads about who is behind the flights.
Officials are keeping quiet about their response. Interior Minister Bernard Cazeneuve told RTL radio today that "the best way to be effective in this area is not to say what we're doing."