The United States has warned Iran against resuming atomic fuel research and development next week, saying if it does not abide by agreements, the international community will have to consider additional steps to restrain Tehran's nuclear ambitions.

"If Iran takes any further enrichment-related steps, the international community will have to consider additional measures to restrain Iran's nuclear ambitions," State Department Spokesman Sean McCormack told reporters. He did not specify what actions the Bush administration will be taking.

His reaction came after the Vienna-based nuclear watchdog International Atomic Energy Agency said it had received a letter from Tehran, saying it would resume nuclear fuel research next week and President Mahmoud Ahmadinejad said that Iran would not 'step back' on this decision.

"In terms of trying to draw a line around something being pure research with respect to enrichment activities, (that) is not something that we're going to buy, and I don't think the international community will either", McCormack said. "The Iranians have really done, sort of, a bob-and-weave on this issue."

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McCormack noted - "They have been seeking to extend out discussions, not really commit to whether or not they are going to negotiate in a serious manner. And, frankly, the patience of the international community is not infinite on this issue because it's a serious one."

"Iran is trying to pursue nuclear weapons under the cover of a peaceful nuclear program. We don't think that that should be allowed to happen and I think you won't find any disagreement on the fact that Iran's obtaining a nuclear weapon would be destabilising to the region and to the world," he said.

McCormack said that the US' view is that if Iran takes any further enrichment-related steps, the international community will have to consider additional measures to constrain Iran's nuclear ambitions - "And I think that Iran should listen very carefully to the international community. It finds itself increasingly isolated on this issue."

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He also said that Iran should 'come clean and cooperate fully with the IAEA'.

The spokesman noted that Washington backed the proposal of Moscow [Images] of the enrichment facilities on the latter's soil as a part of a joint activity, noting that it is a 'a very interesting proposal' and a 'good faith' one.

Complete coverage: The Iran vote and after