A Greenpeace activist on Wednesday flew inside the grounds of a French nuclear power plant using a motorised paraglider, police and the organisation said.

"A Greenpeace activist arrived with a motorised paraglider around 7:40 am (0540 GMT). He flew over the plant, threw a smoke bomb and landed inside, where he was detained," police near the Bugey plant in southeastern France told AFP.

The environmental activist group said the action was aimed at the two men vying for the French presidency in a run-off vote Sunday -- President Nicolas Sarkozy and his Socialist rival and opinion poll frontrunner Francois Hollande.

"The purpose of this action is to send a message to the two candidates in the presidential election who are denying the risk of nuclear power," Greenpeace spokeswoman Sophia Majnoni told AFP.

"We wanted to illustrate an external danger, like a fall of an airplane" into a nuclear plant, she said.

A spokesman for the EDF energy firm that runs the country's nuclear plants said that a lightweight motorised aircraft with one person inside got into the plant, while another person guided the craft outside the facility.

In December, Greenpeace activists broke into two nuclear power plants in France in an action the group said was aimed at exposing the vulnerability of the facilities.

Nine activists broke into the Nogent-sur-Seine plant near Paris and two into the Cruas plant in southern France.