The International Atomic Energy Agency said in February it wasn't given access to the Parchin facility in Iran nor was it able to clarify unresolved issues related to possible military dimensions to Iran's nuclear program.
The IAEA last year said there may be military dimensions to Iran's nuclear research.
Russian Foreign Minister Sergei Lavrov said it was "of principal importance" that IAEA inspectors are present in Iran. He said that while, no illicit activities were verified, sanctions should be lifted only after Iran ensures the international community its nuclear program is intended for peaceful purposes.
"The six nations' (Britain, China, France, Germany, Russia and the United States) approach, voiced several years ago, stipulates that as soon as Iran persuades the world community via the IAEA verification that its nuclear program is absolutely peaceful by nature, it will be vested with all the rights of an IAEA nuclear member state," he was quoted by Russia's state-run news agency as saying.
Iran in September started operations at its Bushehr nuclear plant with the help of Moscow. Russia, under an agreement with Iran, operates and supplies fuel for the Bushehr plant.
Tehran had said it was looking to Istanbul to host April 13 nuclear talks with the Europeans.