"It is clear that we have to extend the deadline. How long, we do not know. It is being studied by experts," said Igor Ivanov, secretary of Russia's security council.

The completion of the power station by Atomstroiexport and the delivery of nuclear fuel by Russia, planned for this year, were delayed by what Moscow had earlier described as financial problems.

Russia had accused Iran of not paying the amounts agreed upon in a deal reached last September on the construction and nuclear fuel supply to the plant, but at the end of March, Moscow acknowledged that Tehran had resumed its payments.

Under the September deal, Russia was to deliver nuclear fuel to Iran in March, the power station would begin working in September and it would start producing energy in November.

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