The international community is ready to help Iran import medical isotopes from abroad, which would make Islamic republic's new uranium enrichment plan "unnecessary", the U.S. State Department has said.

Iran started on Tuesday production of 20%-enriched uranium, which the country claims is needed for a research nuclear reactor in Tehran producing medical isotopes.

During a phone briefing on Tuesday, U.S. State Department spokesman Philip J. Crowley said he hoped the offer would help to "build some confidence" between Iran and the international community and show that Iran's plan to enrich uranium to 20% purity was "unnecessary."

Russia's security chief Nikolai Patrushev said on Tuesday Iran's actions, including its new uranium enrichment plan, "raise concerns among other states, and these doubts are reasonable."

The Islamic republic notified the UN nuclear watchdog of plans to produce higher enriched uranium on Monday, saying it could not wait any longer to reach an agreement on international processing of its uranium for the reactor in Tehran.

Under a plan drawn up by the UN nuclear watchdog last October, the Islamic Republic was to ship out its low-enriched uranium to Russia for further enrichment and subsequently send it to France where it would be made into fuel rods.

The proposal was approved by the six international powers negotiating with Iran over its nuclear program, but Tehran stalled the plan, suggesting it could consider a simultaneous swap of its low-enriched uranium for 20%-enriched uranium, but that the exchange should be simultaneous and would have to take place on its own territory.

On Tuesday, Iranian Foreign Ministry spokesman Ramin Mihmanparast said production of 20%-enriched uranium does not mean the end of a possible fuel swap scheme.

"We can start implementing the swap scheme once our adversaries [Western powers] are ready to recognize our rights," he said.

U.S. President Barack Obama said on Tuesday Washington and its allies were preparing new "significant" sanctions against Iran over its nuclear activities, which Western powers fear are aimed at building weapons. Tehran insists, however, that its nuclear program is designed for civilian power generation.