"In light of the possible (energy crisis) next winter, it is of great importance that the Krsko plant does not shut down by the end of this year but will fulfil in time all the requirements to continue operating," Infrastructure Minister Bojan Kumer told a press conference.

The Krsko nuclear plant, built in 1983 and located 100 kilometres (60 miles) east of the capital Ljubljana near the border with Croatia, had been scheduled to be switched off next year.

But Slovenia and co-owner Croatia decided in 2015 to extend its lifetime for another 20 years, long before the war in Ukraine and EU sanctions on Russia have sparked energy supply concerns across Europe.

Fellow EU countries Belgium and Germany have decided recently to extend the lives of their nuclear power plants to better cope with the current energy crisis.

Activist groups including Greenpeace have demanded the plant's dismantling because of its age and earthquake risks in the region, but the government insists the plant has been upgraded to meet the highest safety and environmental requirements.

Monday's authorisation "shows that there is no safety risks related to the plant's operation," Environment Minister Uros Brezan said.

Slovenia is planning the construction of a second nuclear reactor in Krsko, but the centre-left government has said the final investment decision will be adopted only if its two million citizens back the move at a referendum.

No date for the referendum has been set yet.

The plant covers around 20 percent of Slovenia's electricity needs and 17 percent of Croatia's electricity demand.