Paris - Unidentified drones flew over Paris for a second night in a row, police said on Wednesday in the latest mystery appearance of unmanned aircraft over the French capital at a time of high security.The latest sightings follow a series of drone spottings at French atomic plants last year and, more recently, over the presidential palace and a bay in Brittany that houses nuclear submarines.Authorities have been left scratching their heads as they remain unable to catch any of the operators or determine whether the flyovers are malicious in nature, at a time of high vigilance after last month's deadly Paris attacks.A police source told AFP that witnesses and security forces reported at least five incidents overnight Tuesday to Wednesday over central Paris.Drone sightings reoccurring The tiny aircraft were spotted near the US embassy, not far from the Invalides military museum, the Eiffel Tower and several major thoroughfares leading in and out of the French capital, the source added.Police had already been trying to find out who was behind the appearance of an estimated five separate drone flights over similar areas of Paris the previous night."Is it a game? Scouting for future operations? The investigation will show us," a Parisian police chief said on Tuesday.Authorities were first alerted to mystery drone flyovers in October, when state-run power company EDF filed a complaint with police after detecting the small unmanned aerial vehicles zipping over seven atomic plants.The sightings continued into November, and altogether some 20 flyovers took place over nuclear plants. Their operators were never found.Banned by lawFrench law bans small civilian drones from sensitive areas such as nuclear facilities, which are protected by a no-fly zone that spans a 2.5 kilometre radius and a height of 1 000 metres. Flying the unmanned aerial vehicles over the French capital is also banned by law.In October, a 24-year-old Israeli tourist spent a night in jail and was slapped with a 400-euro fine for flying a drone above the Notre Dame cathedral.Then on 20 January, a pilotless aircraft briefly went over the presidential palace in Paris, not long after three days of jihadist attacks in the capital left 17 people dead and put the country on heightened alert.And at the end of January, small drones were spotted near a bay in Brittany that houses four nuclear submarines - one of the most protected sites in the country.Faced with the difficulty of intercepting drones and their operators, France has launched a one-million-euro programme aimed at developing ways of detecting them.The pilot-less aircraft come in all shapes and sizes, and have a variety of uses, from widely reported military applications to surveillance, film making, 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 the operator can be miles away.