At least five drones were spotted flying over central Paris landmarks during the night and police were unable to catch the operators.
The first drone sighting was near the US embassy in the French capital. The Eiffel Tower, the Place de la Concorde and the Invalides military museum "were also flown over" in the early hours of Tuesday, a security source told AFP.
All the flights were detected between midnight and 6am.
"It could be a coordinated action but we don't know for now," the source, who asked not to be identified, said. "We did everything to try and catch the operators but they were not found," another source close to the investigation said.
(Photo: Screengrab YouTube/Stalin Velasquez)A specialist aviation unit of the police is investigation the reports of the drone flights, but for the moment authorities have no idea who was behind the controls.
A spokesperson from the US embassy refused to comment to The Local on the matter, adding that "the embassy isn't giving any interviews at all".
Earlier this year a drone was spotted flying over the Elysée Palace at night and last year questions were asked about security at France's nuclear power stations after at least drone flights were reported at several plants.
French author and air safety expert Christophe Naudin said: “My hypothesis would be that it is some kind of ‘eco-terrorist’ group, who want to demonstrate how the state is incapable of reacting against this new kind of threat.
“It appears to have been a very well organised operation, involving several drones, that may have been operated manually or on pre-programmed flights,” he said.
“It was done to ridicule the state and the forces of law and order and to show they are not capable of protecting the population," Naudin told The Local.
Naudin believes drones will be a real threat to security in the future.
"One day they will be used for something dangerous," he said. "Currently drones are not developed enough to be able to carry something like a grenade or a bomb but in the years to come they will be. At the moment terrorists don't have the training to be able to use them, but that won't always be the case."
French law bans small, civilian drones from areas such as nuclear facilities, which are protected by a no-fly zone that spans a 2.5-kilometre (1.6-mile) radius and a height of 1,000 metres.
Experts say that the small unmanned craft would not pose a threat if they crashed into a hardened nuclear facility, whose reactors are built to withstand the impact of mid-sized commercial planes.
But the country has nevertheless launched a one-million-euro ($1.1-million) programme aimed at developing ways of detecting and intercepting them.
Drones come in all shapes and sizes, and have a variety of uses, from widely reported military applications to surveillance, filmmaking, sports, disaster relief and scientific research.
The most basic unmanned aircraft are radio-controlled by someone nearby, but other more sophisticated models can be pre-programmed, and these are widely available for just 350 to 400 euros ($440 to $500).