Swedish energy group Vattenfall is demanding 30 billion kronor (3.5 billion euros, $4.6 billion) in damages from Germany following Berlin's decision to shut some nuclear reactors, media reported on Friday.

"Vattenfall has launched proceedings against Germany for more than 30 billion kronor," business daily Dagens Industri wrote, without citing any sources.

The group claims its right of ownership was violated by Berlin's decision in March last year to immediately shutter some nuclear reactors, including the plants in Brunsbuettel and Kruemmel in the north of the country that were jointly owned by Vattenfall and Germany's E.ON.

At the time, two weeks after Japan's Fukushima disaster, the two plants had a history of technical problems and had been out of service since 2007 and 2009, respectively.

Vattenfall has never revealed a cost estimate for the closure, unlike E.ON which has put the cost at eight billion euros.

Vattenfall declined to comment when contacted by AFP.

Sweden's Minister for Financial Markets, Peter Norman, who oversees Sweden's state-owned companies, told AFP the dispute was beyond his remit. "We treat Vattenfall in many respects as a private company. That is a question for a Board," he said.