Unidentified drones have been spotted flying over Paris several times in the last few weeks, most recently over a sensitive military site near Paris over the weekend. The drones have been seen flying near nuclear facilities, government buildings, embassies, major roads and the Eiffel Tower, according to French police.

A small drone was seen making three flights over the Sainte-Assise naval communications center late Saturday night, police said Sunday. A police helicopter dispatched to the scene reportedly failed to find the intruder. The sensitive facility is responsible for handling communications with French submarines at sea. Police authorities told The Telegraph that this is the first such incident they were aware of, but anonymous sources reportedly told Le Parisien that more than one flight, including a crashed drone, had been seen over the complex before. French authorities remain on high alert after three days of shootings in Paris left 20 dead, and France plans to add nearly 3,000 jobs in counterterrorism.

French Interior Minister Bernard Cazeneuve said last week that at least 60 such drone sightings have been reported since October, PressTV reported. Authorities say they do not know who is behind the night-time flights, and cannot confirm if they are malicious in nature, but say the drones are too flimsy to carry weapons or explosives.

In October and November, several drone flights were reported over French nuclear plants. State-run power company Electricity of France filed a complaint after detecting drones flying over seven nuclear plants across the country. Drones were also spotted near a nuclear submarine facility in the Brittany region, in the country's northwest.

Police have said they will hunt down the operators of the drones, but have not been able to catch any of them so far, Reuters reported. "We need to be very vigilant on this, we're going to have to be extremely careful," government spokesman Stephane Le Foll reportedly told France Info radio. "The day that we find the people who are doing this, there will be penalties ... We will find them, sooner or later."

In one incident, witnesses reported seeing three men retrieve a drone and drive off in a black car before authorities could find them, sources told police, according to Reuters. In February, three journalists from Al Jazeera were arrested for illegally flying a drone over the Bois de Boulogne area in Paris, but they are not believed to be linked to the other flights.

French law bans all aerial vehicles from flying within three miles of nuclear facilities. Unlicensed drone flights are illegal over Paris, punishable by a one-year prison sentence and up to $85,000 in fines.