"We always reserve the right as a member of the Security Council to take that matter to the Security Council," despite a deal for Iran to freeze all uranium enrichment, said White House spokesman Scott McClellan.

At the State Department, spokesman Richard Boucher said Washington had strong "reservations" about Iran's agreement with the UN nuclear watchdog agency, which confirmed that the Islamic republic had halted such activities.

"We haven't sprung new faith in Iran's bona fides or Iran's willingness to do this. We are still as skeptical about Iran as we always have been," Boucher told reporters.

Earlier, the Vienna-based International Atomic Energy Agency (IAEA) said it had verified that Iran was fulfilling its pledge to suspend all uranium enrichment, which can be a key step on the road to getting atomic weapons.

The IAEA's 35-nation board of governors also adopted by consensus a resolution hammered out by France, Britain and Germany, endorsing the total freeze, agency spokesman Mark Gwozdecky told reporters in Vienna.

"Iran has failed to comply with its commitments many times over the course of the past year and a half, and for this agreement to succeed, the Europeans, the IAEA and the IAEA board of governors, as well as all members of the international community, will need to remain vigilant," McClellan warned.

Iran had demanded to exempt 20 centrifuges from a November 7 deal with Britain, France and Germany to freeze all such activities -- a move that had threatened to doom the agreement and had drawn sharp US condemnation.

"They have now agreed to a full suspension, including testing and development. All right, we'll see if they do it," said Boucher. "If they do violate it, or, in the pure skeptic's view, when they violate it, it will be reported and that will be the basis for further action."

Asked whether the United States believed Iran should be referred to the UN Security Council because of past violations, he replied: "Yes. And furthermore, if they don't abide by this suspension, then that in itself would be cause enough for referral."

The IAEA adoption of the resolution ended an intense week of back-door talks to save the overall agreement, under which Tehran agreed to freeze all activities that could be used to develop nuclear weapons.

Under the compromise, Iran dropped its demand to exempt the centrifuges, while the resolution did not demand that the Islamic republic be taken to the UN Security Council for possible sanctions, as the Washington had wanted.

The United States says oil-rich Iran does not need a civilian nuclear program to generate energy, and that any activities must be a cover for a covert weapons program. Tehran denies the allegation.

But McClellan sidestepped questions about whether the United States believed the resolution had been watered down.

"We've long expressed our views and we've worked closely with our European friends to get Iran to halt its nuclear weapons program. And the international community is speaking very clearly to Iran about our shared concerns," he said.

Meanwhile, Iran's supreme leader Ayatollah Ali Khamenei said his country would press on with its nuclear program and was not afraid of pressure from the United States.

"The people and the officials are not scared of the political threats made by the powers in the service of oppression," Khamenei was quoted as saying by state television in Tehran.

"Iran will never stop its nuclear program, that is our red line," he said.

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