Iran has fiercely criticised Russia for a delay in shipments of nuclear fuel which will put back the launch of Iran's first nuclear power station.
Iran insists it wants nuclear technology for peaceful purposes
Chief nuclear negotiator Ali Larijani said the delay was "deplorable".
The Russian firm building the plant in the city of Bushehr has blamed the hold-up on a lack of payment. Tehran denies having held back payment.
Iran is under pressure over its nuclear programme, after failing to meet a UN deadline to halt uranium enrichment.
Western nations believe Tehran is hoping to develop a nuclear arsenal, but Iran insists its nuclear programme is solely for peaceful purposes.
Russian state-owned firm Atomstroiexport announced on Monday that a shipment of nuclear fuel would not be delivered as scheduled in March because of delays in payment by Iran.
The company also said the launch of the reactor, due in September, would be put back two months to November because of the dispute over financing.
The fuel in question amounts to approximately 100 tonnes of partially enriched uranium.
Mr Larijani said the delay underlined Iran's need to produce its own nuclear fuel, Iran's official news agency reports.
"Russia has to fulfil its promises on time," he said.
"This [situation] shows that there is no proper guarantee on the supply of nuclear fuel and that Iran's insistence and demands in this respect are entirely proper."
Iran's atomic agency denies Russia's claim that it is behind on payments, saying it has met all its financial obligations. It has offered to publish bank documents to prove its point.
Moscow last year backed limited UN sanctions on Iran for refusing to halt uranium enrichment after objections to the Bushehr deal were dropped.
World powers are now considering more punitive sanctions against Iran after it defied a deadline to halt enrichment work.