"The situation surrounding Iran's nuclear program is well known. Tehran continues enriching uranium, including to a 20% level," Andrei Nesterenko said.

He said questions also remained over Tehran's implementation of the relevant UN Security Council resolutions.

He reiterated Russia's support for the efforts of the International Atomic Energy Agency (IAEA) to clarify all aspects of Iran's nuclear program and ensure its full cooperation on the remaining questions.

Under a tripartite uranium swap deal signed by Brazil, Turkey and Iran on May 17, Iran will swap in Turkey 1.2 tons of its low-enriched uranium for 120 kg of 20% enriched uranium fuel.

The deal did not halt discussions by the Iran Six (Russia, the United States, Britain, France, Germany and China) on a draft Security Council resolution to expand sanctions against Iran over its nuclear program.

International pressure on Iran increased in early February when Tehran announced it had begun enriching uranium to 20% in lieu of an agreement on an exchange that would provide it with fuel for a research reactor.