President Dmitry Medvedev said Monday that Iran was gaining the ability to build a nuclear bomb, remarks welcomed in Washington as a sign of growing international unity behind a tough line toward Tehran.
Medvedev's comments were the strongest criticism of Iran's nuclear program to emerge from the Kremlin under either Medvedev or his predecessor, Prime Minister Vladimir Putin.
A major goal of U.S. President Barack Obama's "reset" of relations with Moscow has been winning Russian backing for a tougher international line toward Iran.
"It is obvious that Iran is moving closer to possessing the potential that, in principle, could be used for the creation of nuclear weapons," Medvedev told a meeting of Russia's ambassadors in Moscow.
"Iran is not acting in the best way," Medvedev said.
He called on Tehran to "show openness and cooperate" with the UN nuclear watchdog, the International Atomic Energy Agency.
The United States, major European Union powers and Israel say they suspect that Iran is trying to build atomic weapons under the cover of its civilian nuclear program. Iran denies this and says it has a right to nuclear power.
"This is about as blunt as Medvedev has ever been about Iran's nuclear program and should be taken as a good sign of increased international unity on Iran's nuclear program," an Obama administration official said in Washington.
Urged on by the Obama administration, Russia voted for a UN Security Council resolution on June 9 to impose new sanctions on Iran over its nuclear program. Medvedev said he was still skeptical of sanctions but they could prod diplomacy.
"I have said before that sanctions as a rule do not have the desired results. Their role is to send a signal, to stimulate the negotiating process," Medvedev said.
Resolution of the Iranian nuclear issue would involve a great deal of patience and energy, but the consequences of failure to deal with it would be grave, Medvedev said.
"At the moment, patience is demanded and the speediest resumption of productive dialogue with Tehran," Medvedev said. "If diplomats let this chance go, then this will become a collective failure for the entire international community."