The US President Mr George W. Bush has expressed his concern that Iran might be developing nuclear arms and said the US would take the lead in preventing the spread of weapons of mass destruction.
Senior US officials claim Iran has done little to co-operate with UN inspectors examining its nuclear program. Washington claims that Tehran is violating the 1970 nuclear Non-Proliferation Treaty and should face more international pressure.
Mr Bush pointed out that the International Atomic Energy Agency, the United Nations body overseeing compliance with the treaty's commitments, meets in June. "We'll wait and see what it says," he said at the White House.
If IAEA Director General Mohamed El-Baradei reports that Iran is not in compliance, there could be another nuclear face-off as the United States, already locked in confrontation with North Korea, and the rest of the board decide on a response.
"I've always expressed my concerns that the Iranians may be developing a nuclear program," Mr Bush said, including to Russian President Vladimir Putin.
"One of the things we must do is work together to stop the proliferation of weapons of mass destruction," he added. "It is a major issue that faces the world and it is an issue on which the United States will still lead."
The US assistant secretary of state for non-proliferation, Mr John Wolf, last week said Iran provides "perhaps the most fundamental challenge ever faced by the Non-Proliferation Treaty," the bedrock pact designed to prevent the spread of nuclear weapons.
Mr Wolf accused Iran of conducting "an alarming, clandestine program to acquire sensitive nuclear capabilities that we believe make sense only as part of a nuclear weapons program."