"On nuclear energy, this crisis will have consequences for the way we consider energy security in all EU countries," said Czech Energy Minister Martin Riman, whose country holds the bloc's rotating presidency.

"One of the ways this might happen is to argue in favour of the return of nuclear energy," he told a news conference in Brussels on Thursday.

The debate is already going strong in former Soviet bloc members of the European Union which are highly dependent on Russian gas and have been hit hard by supply cuts in the standoff between Moscow and Kiev.

Even as Russia and Ukraine neared a deal that would lead to a resumption of gas supplies, Slovakia said Saturday it would begin reopening a power generator at the Jaslovske Bohunice nuclear plant because of the cutoff.

The decision was taken "in the interests of Slovakia, industry and citizens" Prime Minister Robert Fico said.

On December 31, Slovakia shut down the last unit of the Jaslovske Bohunice plant in line with a commitment it made as a condition for its 2004 entry into the EU.

"We know that this is a violation of our conditions of membership" in the European Union, he said, but given the circumstances, there is "a risk of a blackout" that must be addressed.

European Commission chief Jose Manuel Barroso had warned Slovakia against the move, saying that the response to the gas cuts was not to go back on promises.

Nuclear energy has long been one of the most sensitive subjects in Europe and it got a boost last year during the oil price boom when it was seen in some countries such as Britain and Italy as a possible alternative.

However, other countries slowly giving up on nuclear energy, such as Belgium, Germany and Sweden, refuse that it be openly touted as a solution for Europe's future energy needs.

Meanwhile other European countries such as Ireland and Spain have never used nuclear energy.

France, by far Europe's biggest nuclear power generator, has promoted its use as a way of reducing greenhouse gases blamed for global warming.

Paris sees the Russian gas crisis as another argument in favour of nuclear energy, not to mention a source for potential new contracts for state controlled power giant Electricite de France.

Currently, nuclear energy generates about one third of the EU's electricity and accounts for about 15 percent of the bloc's total energy consumption.

However, nuclear energy varies by country from accounting for none at all to being the source of 80 percent of France's energy.

But with the EU's dependence on energy imports on the rise, the cut in Russian supplies shows that "nuclear energy should be developed because it is a major guaranteed source in Europe's energy mix," a senior French diplomat said.

However, environmentalists say that increased nuclear energy use is not as good an idea as it may seem.

"Nuclear energy is used to generate electricity while 90 percent of Russian gas imports to Europe are used for heating. They're two different things," said Greenpeace official Jan Beranek.

Also environmentalists point out that while nuclear power may not contribute to greenhouse gas emissions, the long-term problem of disposing of nuclear waste remains a major challenge.

"Moreover, countries such as Bulgaria, Slovakia and the Czech Republic depend on Russian fuel for their nuclear plants which means that the issue of dependence on Russia is not solved.

"These countries would do better to improve their energy efficiency," he said.

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