It is one of the first times Moscow has publicly recognized that Iran might be moving towards a nuclear weapon.

Russia, which has strong economic and military ties with Iran, has traditionally been an ally of Tehran. But it has recently adopted a tougher stance towards Tehran’s nuclear drive, and backed the fourth round of UN sanctions that was imposed last month.

“Iran is moving closer to possessing the potential which in principle could be used for the creation of nuclear weapons,” Mr. Medvedev told a meeting of ambassadors in Moscow.

The U.S. and major European Union powers suspect that Iran is trying to build nuclear weapons. Iran says its nuclear program is peaceful.