Medvedev told Italian Rai television, ahead of this week's G8 summit of world leaders, that Moscow backs what he said was Washington's policy of seeking rapprochement with Tehran after decades of suspicion.
"If I understand correctly, the United States would like to establish more open and more direct relations with Iran," Medvedev said. "We support this choice. It would be counter-productive to resort to other sanctions."
An ally in modern times, Russia is helping Iran build a nuclear power plant and also stood steadfastly behind the Tehran regime despite massive and deadly street protests following last month's disputed presidential election.
Russia's foreign minister, Sergey Lavrov, said in June that the chances of political agreement on Iran's nuclear capabilities had increased since Barack Obama's arrival in the White House.
Moscow has always maintained that there are no plans for Iran to build an atomic bomb, although Western governments have voiced deep skepticism.
US Secretary of State Hillary Clinton threatened severe sanctions in April if multi-national talks with Tehran on the nuclear issue did not bear fruit.