"We will continue to cooperate with Iran in the peaceful civilian nuclear field as there have been no instructions to the contrary by relevant international bodies," foreign ministry spokesman Alexander Yakovenko told reporters.
"Russia is pushing for active cooperation between Iran and the IAEA (International Atomic Energy Association) and hopes that Iran will continue to collaborate with it," he added.
Russia has faced intense pressure over its construction of the Bushehr reactor from the United States, which fears that Iran could use fuel from the reactor for a weapons program, though Washington has toned down its criticism in the past several months.
Iran in December signed up to an agreement with the IAEA providing for surprise UN inspections of its nuclear sites to fend off US accusations that it is preparing a nuclear weapons programme.
Iran's ambassador to Russia, Gholamreza Shafei, also defended the 800-million-dollar Russian contract.
Cooperation between Iran and Russia is "absolutely transparent and is being carried in full compliance with international legislation and the applicable rules," he told the ITAR-TASS news agency.
The Russian foreign ministry official reiterated that Moscow would not deliver any fuel to Bushehr unless Tehran signs an agreement pledging to return all of it to Russia once it is used up.
Russia's atomic energy agency meanwhile predicted that its chief Alexander Rumyantsev would ink the deal when he pays a long-delayed visit to Iran, probably in May.
"The final text is to be agreed during his visit," the agency's spokesman Nikolai Shingaryev told the ITAR-TASS news agency.
Russia provisionally plans to deliver fuel to Bushehr by mid-2005 and plans for the reactor to start operating a year later.