The Pentagon has sought to play down remarks by Defence Secretary Leon Panetta who has suggested Iran's nuclear programme could be on a faster track than previously suspected.
In an interview with CBS News, Panetta said Iran could have a nuclear weapon in a year or possibly sooner and that the timeline might be different if Tehran had a secret "hidden" site.
"It would be sometime in around a year they would be able to do it (build a nuclear weapon)," Panetta said in the interview aired Monday.
"Perhaps a little less. The one proviso is if they have a hidden facility somewhere in Iran," he said.
But Pentagon spokesmen said Panetta was speaking "hypothetically" and that the defense secretary was not suggesting there was new intelligence pointing to secret facilities.
In the interview, Panetta also refused to rule out military action to prevent Iran from obtaining nuclear weapons but unlike previous statements he made no mention of the potential risks associated with a strike that he has warned of repeatedly.
"If they proceed and we get intelligence that they're proceeding in developing a nuclear weapon, then we will take whatever steps are necessary to stop it," Panetta said.
The Pentagon insisted Panetta's view of Iran's nuclear project had not changed and stressed that if Tehran made the decision to produce weapons-grade uranium, it would be detected by UN inspectors who have regular access to the country's facilities.
"Should they make a decision to move to highly enriched uranium, those inspectors would be able to readily detect it," Captain John Kirby told reporters.
"And we would have at that point, plenty of time to react on our own."
A US official, speaking on condition of anonymity, said the country's intelligence agencies had not changed their view on the state of Iran's program.
Panetta's remarks raised eyebrows among weapons experts who track Iran's program, particularly his reference to the possibility of a secret facility.
"It's definitely misleading," said David Albright, president of the Washington-based Institute for Science and International Security.
The likelihood that Iran could have a nuclear weapon within a year was a "low probability" as any shift to weapons-grade uranium would be exposed by inspectors and Israel would almost certainly take military action, he said.
Moreover, it was "not helpful" to speculate about secret nuclear sites without providing evidence, he told AFP.
The lesson from the US experience in the Iraq war, when Washington claimed there were weapons of mass destruction that never materialized, is for US government figures to speak with more caution, he said.
"Senior officials should be more careful," Albright said.
But the Pentagon rejected the criticism.
"The secretary is always responsible when discussing important national security matters," press secretary George Little said in an email. "His comments on Iran have been both nuanced and forthright."
Panetta was asked about "prospective and aggressive time lines on Iran's possible development of nuclear weapons -- and that is only if Iran decides to move in that direction.
"He didn't say that Iran would, in fact, have a nuclear weapon in 2012."