The European Commission offered on Thursday an additional 500 million euros in EU aid for Bulgaria, Lithuania and Slovakia to put Soviet-era nuclear reactors out of service for good.

The three EU states closed down the reactors as part of their deals to join the European Union, but Brussels wants to ensure that the power plants are forever sealed off.

"It is in our citizens' interest that these reactors will be safely decommissioned and that they will never be restarted again," said EU energy commissioner Guenther Oettinger.

"This additional financial support will help the three Member States to timely progress in defueling and decommissioning of these nuclear reactors," he added.

The funds will help the three former communist states continue the safe decommissioning of the nuclear power plants known as Kozloduy (Bulgaria), Ignalina (Lithuania) and Bohunice (Slovakia).

"The Union assistance for decommissioning of nuclear power plants aims at reaching an irreversible state in the decommissioning process and eliminating the major source of radiological hazard," the commission said.

The three nations must fufill certain conditions before getting the EU funds, including fully implementing EU legislation on nuclear safety and the management of nuclear waste.

They must also create legal frameworks to raise the resources needed to cover the remaining financial needs so that they can gradually take over financial responsibility, the commission said.

The EU has committed 2.85 billion euros in financial assistance until 2013. The additional 500 million euros would come in from 2014.

Lithuania will get an extra 210 million euros until 2017, Bulgaria will have 185 million euros more until 2020 and Slovakia another 105 million euros until 2017.