Washington has met an announcement by President Mahmoud Ahmadinejad that major advances have been achieved in Iran's nuclear programme with "scepticism".
"I think we certainly could view it with scepticism," said State Department spokesman Robert Wood, commenting on reports that there are some 7,000 centrifuges installed in Iran to enrich uranium.
"Iran has in the past, you know, announced that it is -- it was running a certain number of centrifuges that didn't really pan out with regard to the IAEA's (International Atomic Energy Agency's) own estimate.
"So it's not clear," he said on Thursday.
For her part, Secretary of State Hillary Clinton said: "Well, first of all, we don't know what to believe about the Iranian programme. We've heard many difference assessments and claims over a number of years."
She added that the United States is involved with talks by world powers with Iran in part to "enforce the international obligations that Iran should be meeting to ensure that the IAEA is the source of credible information."
Clinton pointed to "a great gap between what the IAEA observed about seven weeks -- six, seven weeks ago and what the Iranians are now claiming."
Ahmadinejad on Thursday declared the major advances at the opening of a nuclear fuel plant. At the event he announced that two high-capacity centrifuges were being tested.
