Bulgaria has filed an international arbitration court claim against Russian nuclear company Atomstroyexport over delayed payments, Economy Minister Traicho Traikov said Thursday.

"On Friday, (Bulgaria's power utility) NEK filed its claim in the Geneva-based arbitration court," Traikov told state BNT television, without providing details.

NEK was not immediately available to comment but it had previously said that Atomstroyexport owed it as much as 61 million euros ($81 million) for equipment the Russian state-owned company bought back from the stalled Belene nuclear plant.

Atomstroyexport already took NEK to the International Court of Arbitration in Paris in July, seeking 50 million euros in damages for delayed payments linked to the long-stalled Belene project on the Danube.

Bulgaria hired Atomstroyexport in November 2006 to build a new 2,000-megawatt plant to compensate for lost capacity at Bulgaria's only nuclear power facility at Kozloduy.

Sofia was compelled to shut down four of its six reactors at Kozloduy to secure European Union accession in 2007, leaving just two 1,000-megawatt nuclear units in operation.

Work on the Belene project has stumbled however over price haggling and more recently over safety concerns following the Fukushima nuclear disaster, with Bulgaria still unable to decide on its viability.

Russia insisted Bulgaria should pay as much as 6.3 billion euros for Belene's two reactors, while Bulgaria has demanded a price of about 5.0 billion euros.