John Bolton, Under-Secretary of State for Arms Control and International Security, told BBC radio that military action was a last resort but insisted that Iran could not be allowed to develop a nuclear weapons capability.
Interviewed on the BBC's Today program, Mr Bolton said that US President George W Bush "has repeatedly said that all options are on the table. But that (military action) is not only not our preference, it is far far from our minds."
Pressed on whether military action remained a possibility, Mr Bolton said: "It has to be an option."
"Nuclear weapons are incredibly dangerous and when you couple the Iranian nuclear program with their aggressive efforts to expand the range of their ballistic missiles, they are bringing more and more of our friends and allies within range," he said.
Mr Bolton added: "What our objective is now is to stop the Iranian nuclear weapons programme before they achieve a weapons capability.
"They are pursing multiple routes to nuclear weapons and we need to get that stopped."
Iran says it is seeking nuclear power for civilian uses, a position Washington has overtly rejected.
Iran has no plans: Putin
Meanwhile, Russian President Vladimir Putin says he believes that Iran has no plans to develop nuclear weapons.
Mr Putin says he was personally assured by Iranian President Mohammad Khatami two days ago.
He also says he believes that Iran is ready to submit its nuclear energy programme to full monitoring by the International Atomic Energy Agency.
Mr Putin says Russia stands by the US in opposing the development of weapons of mass destruction.
"Russia's position and the position of the US on this regard is much closer than it seems at first glance," he said.
"We proceed from our principle position in accordance with which we [are] categorically against the spread of the proliferation of the mass destruction weapons on our planet.
"We are for the reinforcement and strengthening of non proliferation regimes."
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