Moscow: A senior Russian government official said on Monday that the United States was hindering the resumption of talks with Iran on a fuel swap deal aimed at easing concern over the Islamic Republic's nuclear ambitions.

The comments, made to a discussion group of Russia experts, appeared aimed at nudging Washington towards restarting stalled UN-backed talks to provide Iran with nuclear fuel for a Tehran research reactor.

"I am concerned by the fact that the United States slowed down the process," the senior government official told the Valdai group of Russia experts when asked about the fuel deal.

The official spoke on condition of anonymity because of the sensitivity of the issue.

Western powers suspect Iran is trying to develop nuclear weapons, a fear heightened by its move in February to start enriching uranium to a level of 20 per cent from about 3.5 per cent previously, taking it closer to weapons-grade thresholds.

But the Russian official said Western demands that Iran give up making low enriched uranium were futile and that major powers should instead focus on preventing Tehran getting fuel that could be used for a nuclear bomb.

"It is not realistic that Iran will give up the enrichment up to four per cent," the official said. "The international community should focus on preventing the further enrichment to 20 per cent."

Fuel swap?

Iran has given a range of sometimes conflicting responses to the fuel swap deal, underscoring concerns in Western capitals and in Moscow that Tehran is drawing out the process to gain time while it continues push ahead with enrichment plans.

Iran denies that it is seeking to make nuclear weapons and says that it was forced to enrich to higher levels after talks for a fuel swap deal with the United States, Russia and France stalled last year.

Russia welcomed a statement last month by Iranian President Mahmoud Ahmadinejad, who said work to make higher-grade uranium would stop if it got assurances on nuclear fuel supplies for the Tehran research reactor.

At that time, Russia also called for a meeting as soon as possible to discuss such supplies.

President Dmitry Medvedev has toughened Moscow's criticism of Iran over the past year, telling Tehran it must explain the "military components" of nuclear programme.

The Russian official said Moscow did not want Tehran to have nuclear weapons but warned that rash decisions over Iran could lead to a tragedy for the Middle East.

Since 2005, the United Nations nuclear watchdog has been probing Western intelligence reports indicating that Iran has coordinated efforts to process uranium, test explosives at high altitude and revamp a ballistic missile to make it suitable for a nuclear warhead.

Russia voted for a UN Council sanctions resolution against Iran in June but Moscow has criticised tougher additional sanctions imposed by the United States and the European Union.

The Russian official said the tougher unilateral sanctions imposed by Washington and Brussels were unacceptable.

"If we agreed on something we shall not allow any step to the left or right of the basic document," the official said.