Bulgarian Energy Minister Temenuzhka Petkova has announced the country deems "miscalculated" an interest rate on payments ordered by an international arbitration to Bulgaria over an abandoned nuclear plant.

Under the ruling in June, Bulgaria has to pay hundreds of millions of EUR to Atomstroyexport, the export arm of Rosatom, for the equipment and reactor it has produced for Belene nuclear power plant (NPP).

Belene NPP was scrapped by the previous government of Prime Minister Boyko Borisov.

Petkova has told reporters prior to an energy forum that a "technical mistake" had allowed the arbitration court to set a "compound interest", thus infringing Bulgaria's national law, specialized website 3e-news.net quotes her as saying.

"Compound interest" is calculated on both the initial principal and interest already accumulated from previous periods of a deposit or a loan.

The interest rate calculated for the period after July 02 may need clarification, she has added.

The minister has made clear that the sum owed by Bulgaria might have to be reduced, but has stopped short of naming a new figure.

The dispute concerns a sum of EUR 82 M and the way it is calculated, she has made clear.

The initial principal in the arbitration's ruling was EUR 500.841 M as of mid-June, with a daily interest rate of EUR 0.167 M.

Russia claims the sum is EUR 620 M.