The comments by Under Secretary of State John Bolton come amid reports that the United Nations nuclear watchdog has found undeclared plans for nuclear technology in Iran.
Western media quoted diplomats as saying the International Atomic Energy Agency (IAEA) has found designs for an advanced centrifuge that should have been mentioned in Iran's October 2003 declaration of its atomic program.
Bolton said the finding shows Iran continues to pursue nuclear weapons.
"The information that the IAEA has learned is certainly consistent with the information that we had, and it's not surprising. It's another act of Iranian deception and not something that leads to any feeling of security, that they are carrying through on their commitment to suspend enrichment activity," Bolton said.
Iran has always denied it is seeking to build a bomb, a stance Foreign Minister Kamal Kharrazi repeated yesterday in Rome.
"We do not think that a nuclear weapon is going to bring us more security. It's not part of our doctrine. That is why we have signed the Additional Protocol, because we do not have anything to hide, and we are ready to be inspected more severely by the IAEA inspectors," Kharrazi said.
But the finding, reportedly made during IAEA inspections, throws into question Iran's promise in October to come clean on its nuclear program and suspend the enrichment of uranium.
Other questions, too, are raised by the discovery of the plans for the so-called G2 centrifuge, which is capable of producing material for nuclear weapons.
Pakistan is also known to have this centrifuge. Last week, the founder of Pakistan's nuclear program, Abdul Qadeer Khan, admitted trading nuclear secrets to Iran, Libya, and North Korea on the black market.
Shannon Kile is a nonproliferation expert at Stockholm's International Peace Research Institute.
"What [the finding] does indicate is that it's much more difficult for Iran to deny plausibly that it doesn't have a nuclear weapons program under way. What's especially worrying is that we know that Pakistan's middlemen had supplied Libya not only with the same type of plans for a gas centrifuge but also for an actual weapon design, and what we don't know is whether or not the Pakistanis have also supplied Iran with a nuclear weapon warhead design. And that, I think, is what will be at the forefront of the IAEA activities to find out," Kile said.
The finding may also lead to calls for the IAEA to report Iran to the UN Security Council, which could impose economic sanctions.
But outside the U.S., other nations are so far reserving judgment.
Russia said yesterday there's no evidence Iran is seeking a nuclear bomb. Atomic Energy Minister Alexander Rumyantsev said Moscow will sign a deal next month to ship nuclear fuel to Iran's Bushehr plant -- something Washington has repeatedly asked Moscow not to do.
"It's another act of Iranian deception and not something that leads to any feeling of security, that they are carrying through on their commitment to suspend enrichment activity."
And British Prime Minister Tony Blair said he'd rather wait until the IAEA comes out with its report on Iran next month.
"The good thing about the situation we helped to bring about is that the International Atomic Energy Agency are now committed in Iran and will produce a report, I think, in March, and that is a report that can go through all these issues. I think probably rather than me commenting at this stage, we should wait until they make their report then," Blair said.
The developments surrounding Iran's nuclear program cap a week in which weapons proliferation has repeatedly dominated the news.
On 11 February, U.S. President George W. Bush called for tighter international controls to stop the spread of nuclear technology.
Yesterday, the head of the IAEA, Muhammad el-Baradei, backed Bush's call for a crackdown on the nuclear black market. But he also called on the world's big nuclear powers -- like the U.S., Britain, and Russia -- to move toward disarmament.