Tehran has been given until 31 October by the International Atomic Energy Agency (IAEA) to dispel international suspicion over its nuclear ambitions.
But in remarks that will appear to some observers as displaying a remarkable lack of tact US Undersecretary of State John Bolton said:
"I think what will happen prior to October 31st is the Iranians will cooperate a little bit and the issue will be, 'Did they cooperate enough?"
He added: "They will try and throw sand in our eyes and use a modest level of cooperation to hide some level of obfuscation and lack of cooperation, to conceal as much as they can, to delay, to fight for time, and to avoid having the issue referred to the (UN) Security Council."
The comments could give critics of the US fuel to claim that Washington has already made up its mind about Iran and is preempting the IAEA deadline.
Critics of the US-led invasion of Iraq have accused Washington of cutting short the work of United Nations weapons inspectors in deciding Saddam Hussein was in breach of UN resolutions to give up his alleged weapons of mass destruction.
The IAEA is demanding rigorous inspections of suspected sites because of suspicions Tehran is secretly developing nuclear weapons.
Iranian President, Muhammad Khatami, insisted on Wednesday Tehran will provide whatever cooperation is needed to prove its nuclear programme is solely geared to producing electricity.
But Bolton predicted that if unchecked, Iran could have a nuclear weapons capability "towards the end of the decade", though some people theorise it could be much sooner.
Muhammad al-Baradei is pressing
Iran for tougher inspections
"The risk of outward Iranian proliferation of weapons of mass destruction to other countries in the region is also a risk we take very seriously," he added.
Asked why Washington did not take a similar line on Israel's nuclear programme, Bolton said: "The issue for the US is what poses a threat to us and to our allies...We are not platonic guardians, we are representing American interests."
The Proliferation Security Initiative has won support from 10 other nations, helping ease diplomatic tensions over the US-British invasion of Iraq and the subsequent failure to find weapons of mass destruction there.
Bolton has said deposed Iraqi dictator Saddam Hussein may well have got rid of his weapons.
"In the short term we don't entirely know what Saddam may have done with the weapons of mass destruction. They may have been moved out of Iraq years ago - it's possible," he said.
Saddam may also have ordered them destroyed, he added, "in which case it was a bad mistake not to keep records".
The existence of about 1000 nuclear scientists whom Saddam dubbed his "nuclear Mujahideen" demonstrated Baghdad's dangerous intentions, Bolton added.