The US Secretary of State, Colin Powell, says Iran has a more developed nuclear weapons programme than had previously been thought.
Washington says Iran is part of an "axis of evil"
He said it showed that a nation intent on producing a nuclear weapons programme could conceal it from inspectors and outsiders - which he used to draw a parallel with the situation in Iraq.
His comments came after US news magazine Time quoted diplomatic sources as saying that a nuclear power facility at Natanz in Iran was near to producing enriched uranium that could be used in nuclear weapons.
We have seen this week Iran has got a more aggressive nuclear programme than the IAEA thought it had
US Secretary of State
Iran, which Washington has branded an "axis of evil" member along with Iraq and North Korea, last month unveiled plans for
an ambitious nuclear energy programme. But it has insisted its aims are purely peaceful.
"Here we suddenly discover that Iran is much further along, with a far more robust nuclear weapons development programme than anyone said it had," Mr Powell said on US television.
"It shows you how a determined nation that has the intent to develop a nuclear weapon can keep that development process secret
from inspectors and outsiders, if they really are determined to do it, and we know that Saddam Hussein has not lost his intent."
The discovery that Iran has been trying to
acquire nuclear weapons and to enrich uranium did not surprise Washington, US national security
adviser Condoleezza Rice said.
"It's been couched as a peaceful programme. But we've been for a long time one of the lone voices that has said that the Iranians are a problem," she told ABC.
Time Magazine quoted diplomatic sources as saying work on the Natanz plant "is extremely advanced".
It said the plant involves "hundreds" of gas centrifuges ready to produce enriched uranium that could be used in advanced nuclear weapons and "the parts for a thousand others ready for assembly".
On Saturday, Iran agreed to provide early information about any plans to build new nuclear facilities.
First nuclear plant comes online by summer 2004
Has signed up to the
Nuclear Non-Proliferation Treaty
Can now supply its own power stations with nuclear fuel
President Mohammad Khatami said his country meant to develop its nuclear industry in line with the nuclear Non-Proliferation Treaty (NPT) and would further co-operate with the International Atomic Energy Agency (IAEA), to avoid any "misunderstandings".
The head of the UN's watchdog, Mohamed ElBaradei, was in Tehran at the weekend to discuss Iran's controversial nuclear programme.
Two IAEA officials remain in Iran until Wednesday to visit another nuclear site at Arak.
Last month, Iran announced it had discovered uranium deposits and had started mining near the central city of Yazd.