Around 30 Greenpeace activists were arrested on Monday after breaking into an EDF nuclear power plant in southern France, saying they wanted to expose security flaws and demanding its closure.

Interior Minister Manuel Valls called for an investigation into the intrusion which raised questions about the security of France's 19 nuclear plants and 58 reactors.

The action echoed tensions between the Socialist government and ecologists, who accuse Hollande of not doing enough to reduce France's reliance on nuclear power and increase the use of renewable sources of energy.

The president has pledged to cut the share of nuclear energy in the country's electricity mix to 50 percent from 75 percent by 2025. He has also said he wants to close the country's oldest plant at Fessenheim, near the German border, by 2017.

Greenpeace said to honor his promise, Hollande would have to close at least 10 reactors by 2017 and 20 by 2020. The campaign group said this ought to include Tricastin, which was built more than 30 years ago. However, France's nuclear safety agency ASN did not include Tricastin in a list released in April of six nuclear plants with the lowest safety performance in 2012.