"The president made it pretty clear, he said previously that Iran is not Iraq," spokesman Scott McClellan told reporters when asked if Washington might use force against Iran.

"We're working with the international community to solve this in a peaceful and diplomatic manner, that's what we've been doing and continue to do," McClellan said after Iran announced it had resumed sensitive atomic research.

But, he added, "in terms of options ... he (Bush) never takes options off the table."

Earlier, McClellan warned that resuming uranium enrichment and reprocessing activities "would be a serious escalation of the nuclear issue."

McClellan said the US administration was pursuing talks with Britain, France and Germany, the so-called EU-3 which are trying to negotiate a solution to the nuclear standoff.

But he added that if Iran breaches its international obligations, "there's no other choice but to refer the matter" to the UN Security Council for possible sanctions.

The United States fears Iran's civil nuclear program is a cover for developing a nuclear bomb. Tehran denies it, insisting the program is designed solely to meet its electricity needs.

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