"We cannot accept the re-opening of this unsafe reactor at Bohunice," Environment Minister Nikolaus Berlakovich said in a statement.

"In a community, agreements must be respected. The (plant's) shutdown was a key condition (to Slovakia's entry into the EU) for us and can't just be erased," he added.

"Now it's up to the European Commission to strongly urge compliance with the accession agreement."

In a rare moment of unity, opposition leaders from the two far-right parties and the environmental Greens party also blasted the decision, arguing that Bohunice was "one of the three most dangerous nuclear plants in Europe" and urging the Austrian government to take legal and diplomatic measures against Slovakia.

Austria, a strong opponent of nuclear power, has often complained of nuclear plants in neighbouring countries and the potential repercussions for the small alpine state.

Slovakia announced Saturday it would begin reopening a power generator at Jaslovske Bohunice, which was only entirely shut down on December 31 as part of a commitment to the European Union before its 2004 entry into the bloc.

"We know that this is a violation of our conditions of membership" but there is "a risk of a blackout" due to the gas stoppage that must be addressed, Prime Minister Robert Fico said.

Austrian Greens party leader Eva Glawischnig hit back: "The gas crisis should not allow countries to re-open dilapidated reactors or continue risky nuclear technology under the excuse that there's a power shortage: that's playing with fire."

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