Medvedev, who will arrive in Washington later Monday for a two-day summit on nuclear security hosted by US President Barack Obama, warned that energy sanctions on Iran could lead to "humanitarian catastrophe," despite the popularity of such measures among US lawmakers.
"If we're talking about energy sanctions, I'll tell you my opinion. I don't think on that topic we have a chance to achieve a consolidated opinion of the global community on that," Medvedev told ABC News television.
"Sanctions should not be paralyzing. They should not cause suffering."
The handpicked successor of ex-president and current Prime Minister Vladimir Putin said Iran's nuclear program "is not transparent" and should be monitored carefully.
If world powers slap a fourth round of UN sanctions on Iran, they should be smart and effective because previous ones often have not worked, he said.
"They should not lead to humanitarian catastrophe, where the whole Iranian community would start to hate the whole world," Medvedev added.
Russia has joined an effort led by Washington to toughen sanctions within weeks on Iran over what the United States and its allies say are efforts to produce nuclear weapons under the cover of what Iran insists is a civilian energy program.
"Are they pursuing the nuclear weapon or not? I don't know," Medvedev said. "But we should carefully monitor it."
He said Iran's efforts to enrich uranium on its soil despite an offer by the major powers to supply the fuel "could be considered as at least the desire to enter into conflict with the world community."
Uranium enrichment is the sensitive process that lies at the heart of Western concerns about Iran's nuclear program. It can produce the fuel for nuclear reactors but in highly extended form can also make the fissile core of an atomic bomb.
Iranian President Mahmoud Ahmadinejad gave instructions in February for Iran to begin enriching uranium to the 20 percent level required for a Tehran medical research reactor after long-running international talks to supply the fuel from major powers failed to bear fruit.
The ABC interview was conducted on Friday, a day after Medvedev and Obama signed a nuclear arms reduction treaty in Prague. It first aired on Monday.
