On Wednesday, French authorities tried to determine who controlled a number of unmanned aircraft that had flown over Paris for the second night in a row, Agence France-Presse reported.

Operating drones over the French capital is illegal in the dark, but witnesses and security forces reported at least five sightings in the night from Tuesday to Wednesday. They were seen near landmarks such as the Eiffel Tower, the Invalides military museum, the U.S. Embassy and major thoroughfares leading in and out of the city.

Police have set up a 10-strong team of investigators to determine their operators, the BBC noted.

Government spokesman Stephane Le Foll told AFP that a probe was under way.

"People should not be worried but vigilant," Le Foll said. "It's an issue which is taken very seriously."

Authorities are in a frenzy to determine whether the flyovers are the work of pranksters, tourists or something more malicious. The French public has been on alert ever since the January attacks on the Charlie Hebdo satirical magazine and a Kosher grocery store in Paris, and a series of suspicious drone sightings already stoked fears last year.

Unmanned aircraft have been observed at atomic plants and over a bay in Brittany that houses nuclear submarines. At one point, they overflew the Elysee Palace, the French president's official residence in the capital.

Local laws prohibit flying any aircraft lower than 19,700 feet over central Paris unless city authorities grant a special permission, the BBC explained. That includes drones, which are banned altogether outside daylight hours.

Their inherent security threat, however, is reportedly minimals. Small drones, such as the ones believed to have been used in Paris, are not strong enough to be outfitted with a significant payload of explosives. Meanwhile, higher-quality bird's-eye images of landmarks than the ones they could produce are already readily available online.

The main reason for the nighttime ban is that an unmanned aircraft might get out of control and crash onto a street, injuring a pedestrian or causing a car accident.

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