Russia says an offer to visit Iran's nuclear sites "deserves attention" but does not replace the need for regular inspections.
Russian Foreign Minister Sergei Lavrov said Thursday the visits proposed by Tehran "must not be viewed as a substitute" for inspections by the International Atomic Energy Agency.
He also said there is still a need for Iran to hold talks with Germany and the five permanent members of the U.N. Security Council - Britain, China, France, Russia and the United States. Those talks are scheduled for Istanbul on January 21-22.
Iran had invited foreign diplomats to visit its atomic sites a week before the Istanbul meeting.
China on Thursday said it is unlikely to accept the offer, saying it would be difficult for the country's nuclear envoy to visit Iran.
Iran says its nuclear program is for peaceful means, but the country has been facing international sanctions amid fears Tehran is developing nuclear weapons.
The European Union has already declined the tour, which Iran said would include the Natanz uranium enrichment plant and the Arak plutonium-producing heavy water complex.
Iran says it is willing only to discuss a nuclear materials swap at the Istanbul meeting.
EU foreign affairs chief Catherine Ashton will visit Turkey this week in preparation for the talks.