The war in Ukraine hasn't deterred Hungary's interest in the project to add to the four reactors already operating at the Paks site outside of Budapest.

The fact that it is moving forward is another indication of the close ties between Hungary's nationalist Prime Minister Viktor Orban and Russian President Vladimir Putin.

"This is a big step, an important milestone," said Foreign Minister Peter Szijjarto said on his Facebook account after the national regulator issued Thursday a permit following numerous delays.

"We can now move from planning stage to construction. You'll see that at the Paks site in the coming weeks," said Szijjarto.

He added it is "realistic" the new reactors could enter service by 2030.

The 2014 deal to build two 1,200 megawatt reactors at the plant in Paks, 100 kilometres (60 miles) south of Budapest, will more than double its capacity.

Built with Soviet-era technology in the 1980s during Hungary's communist period, the plant is the sole nuclear facility in the EU member, and currently provides around 40 percent of its electricity needs.

"In this manner we will ensure Hungary's energy security in the long term and protect Hungarians from wild swings in energy prices," said Szijjarto.

Russia is financing most of the project with a 10-billion-euro ($10-billion) loan to Hungary, which is paying for the remaining 2.5 billion euros.

Fellow EU member Finland cancelled a similar Russian nuclear power plant project in May over Russia's invasion of Ukraine.

Hungary has bucked EU efforts to isolate and sanction Russia.

Whereas its EU partners are trying to quickly wean themselves off of Russian oil and gas, Hungary has obtained exceptions and has negotiated extra deliveries of natural gas.