The European Union has rejected a plea from Balkan countries to restart two reactors at the Kozloduy nuclear plant in Bulgaria to ease power shortages.
Bulgaria has closed four of the six reactors at the Soviet-era plant
Five states asked the EU on Monday to allow Bulgaria to resume electricity production at units three and four.
The reactors - deemed unsafe by the EU - were closed by Sofia on 1 January, as part of its EU accession treaty.
But now Bulgaria says they are safe and would provide much-needed electricity for the Balkans.
The European Commission told BBC News that it had not yet considered the Balkan proposal, but Ferran Tarradellas, spokesman for the EU energy commissioner, said that conditions had not changed.
"Bulgaria has undertaken a commitment to close units three and four in Kozloduy as part of the accession treaty," Mr Tarradellas said.
He added that the EU had already provided hundreds of millions of euros in assistance to Bulgaria to soften the blow of the closure.
The chief European Commission representative in Bulgaria, Michael Humphreys, acknowledged that Bulgaria's decision to close the two Soviet-built reactors had been difficult.
But he told BBC News that "any request to change that decision would be unacceptable, because it would entail a renegotiation of the accession treaty, a unanimous consent of the 27 member state governments and ratification by 27 parliaments".
Bulgaria also closed down two old reactors at Kozloduy in 2003, leaving just two of the six there still in action.
But Bulgaria plans to complete construction of a new nuclear plant at Belene, also by the River Danube.
Bulgaria's Economy and Energy Minister, Rumen Ovcharov, expressed his country's preoccupation with the worsening energy situation.
Bulgaria, Serbia, the Former Yugoslav Republic of Macedonia, Albania and Croatia adopted a declaration on Monday in Sofia in which they warned of dire consequences if the two reactors were not reopened. The plant has
"We are concerned about the current electricity supply problems of the region, which could result in higher economic and political instability," the statement said.
Bulgaria exported 7.8 billion kilowatt-hours of electricity in 2006, which is roughly what the two nuclear reactors in Kozloduy produced.
Albania and Kosovo have experienced power cuts in the last few years, but many of these cuts are caused mainly a by lack of investment in the power infrastructure.
The statement issued by the Balkan countries claimed that electricity prices had jumped 80-100% compared with last year.