When asked by reporters how close Iran was to having a nuclear weapon, Dvorkin, a retired general and veteran player in US-Soviet disarmament talks in the 1970s and 1980s, said “One can speak of one or two years.”

Dvorkin, who voiced his personal views and not those of the Russian government, contradicted US intelligence reports and his own government’s view that Iran is still far from having a nuclear weapon.

“In the technical sense, what may be holding them back is the lack of enough weapons-grade uranium,” Dvorkin said.

More importantly, “I consider this a significant threat” because Iran “has effectively ignored all the resolutions and sanctions imposed by the United Nations Security Council”. As “a nuclear state [it] would become untouchable, allowing it to broaden its support” for organisations such as Hamas and Hizbollah.

Officially, Russian diplomats have downplayed US and Israeli fears that Iran is on the verge of building an atomic weapon, while Moscow has resisted calls for tougher sanctions on Tehran for its disputed nuclear programme.

Similarly, Iran’s clerical rulers have continued to claim that their nuclear programme is entirely peaceful.

In developing this programme Russia has played an important role by helping to build a civilian nuclear power plant in Bushehr, which is now finished and undergoing testing.

Early this month the International Atomic Energy Agency (IAEA) accused Tehran of concealing 209 kilos of uranium, noting that it was unable to achieve any "substantive" progress in the investigation intended to reveal whether Tehran's nuclear programme has military aspects.

“Regrettably,” said an IAEA statement, “as a result of the continued lack of cooperation by Iran in connection with the remaining issues which give rise to concerns about the possible military dimensions of Iran's nuclear programme, the agency has not been able to make substantive progress on these issues.”