French police are investigating a number of incidents over their nuclear power stations in recent weeks, as unmanned drones buzzed the plants. Greenpeace, who have pulled similar stunts in the past deny involvement in the “large-scale operation”.

Flying any craft within a three mile radius of a nuclear plant is illegal in France, but between October 5th and the 20th there were multiple incidents of remote-controlled drones flying over the stations themselves. On one occasion, there were drones flying over four sites across the country simultaneously, suggesting the drones were not operated by a lone wolf, and there is a concerted espionage effort under way. Seven sites have been targeted so far by the commercially-available aircraft.

Environmentalist pressure group Greenpeace, who object to nuclear power have spent years attempting to erode public confidence in the clean energy source, are dedicated to pointing out purported security weaknesses in the plants. TheLocal.fr reports that in 2012 the group used a remote drone to film a Greenpeace activist para-glide over the outer fence and land inside a nuclear plant in eastern France to highlight the danger of attack from the air.

Watch: Greenpeace flies into nuclear plant

Despite their own recklessness in the past, Greenpeace expressed concern about the flights, as they may be a vindication of the security weaknesses they have sought to illustrate. A spokesman called it “a large-scale operation”. Greenpeace claim the government is playing down concerns, and say a drone has also overflown the nuclear research institute in Paris.

The French authorities stated at this stage the drones had not affected “the safety or the operation” of the countries nuclear infrastructure, but efforts were ongoing to “neutralise” the threat of the drones in future. As most small civilian drones are piloted by WiFi or ordinary hobby-band radio, this may include electronic counter-measures at the sites, or even a deployment of military personnel. The French Air Force is the body charged with defending the nation’s nuclear power facilities.