French police block the access at the nuclear plant in Nogent-sur-Seine, 95 kilometres (60 miles) southeast of Paris
Activists from environmental group Greenpeace managed to sneak into a nuclear power plant near Paris on Monday in a move they said highlighted the dangers posed by France's reliance on atomic energy, reports AFP.
Police confirmed the intrusion and said activists had tried to break into two other nuclear sites in the south of France.
French energy giant EDF, which runs the nuclear plants that France relies on for 75 percent of its energy, sought to play down the incident, saying the activists at the plant near Paris had been detected but a decision made not to immediately intercept them.
EDF said activists had unfurled banners at two other sites but did not specify whether they had managed to enter the nuclear plants.
In a statement, Greenpeace said some members had entered the nuclear site at Nogent-sur-Seine, 95 kilometres (60 miles) southeast of Paris, to "spread the message that there is no such thing as safe nuclear power."
"A group of militants managed to climb on to the dome of one of the reactors, where they unfurled a banner saying 'Safe Nuclear Power Doesn't Exist'," said Greenpeace spokesman Axel Renaudin.
"The aim is to show the vulnerability of French nuclear installations, and how easy it is to get to the heart of a reactor," said Sophia Majnoni, a Greenpeace nuclear expert.
EDF insisted it had been aware of the intrusion from the start.
The activists "were immediately detected by the security system and were permanently followed on the site, without a decision being made to make use of force," the company said in a statement.
It said seven to nine people had been "calmly apprehended" by the French gendarmerie, a branch of the armed forces that protects nuclear sites.
Ladders and banners were also found near a nuclear power station in Blaye in southwestern France and at a nuclear research centre in Cadarache in the southeast, the gendarmerie told AFP.
EDF said banners had also been deployed at nuclear power plants in Chinon in central France and at Blayais in south-western France, but "immediately removed." The company did not say whether activists had managed to enter those sites.
Henri Guaino, an advisor to President Nicolas Sarkozy, said the activists' move was "irresponsible" but raised questions about security at nuclear plants.
"It was irresponsible on their part," he told BFMTV. "But this does make one think about the security of access to nuclear power plants. Conclusions must be drawn from this."
The incident comes as some in France have begun to question the country's long-held support for nuclear energy.
France, the world's most nuclear-dependent country, operates 58 reactors and has been a leading international proponent of atomic energy.
But the country's reliance on nuclear energy has been increasingly called into question since the Fukushima disaster in Japan, which prompted Germany to announce plans to shut all of its reactors by the end of 2022.
Ahead of a presidential election next year, Socialist candidate Francois Hollande has agreed a deal with the country's Greens to push to reduce France's reliance on nuclear energy to 50 percent by shutting down 24 nuclear reactors by 2025.