"It looks like there is some progress, but to determine whether or not the progress is real there must be verification," he said during a joint public appearance with Colombian President Alvaro Uribe.

"We look forward to seeing that verification," said Bush, who has long charged that oil-rich Iran does not need civilian nuclear power and therefore must be using its atomic programs as cover for a secret weapons program.

The Islamic republic announced earlier Monday that it would suspend its uranium enrichment activities in a bid to soothe international fears over its suspected nuclear weapons programs and to avoid possible sanctions.

"Let's say I hope it's true," said the US president, adding that verification of that claim was needed if the Iranians were to "earn the trust of those of us worried about them developing a nuclear weapon."

"That's just not the United States, it's France and Great Britain and Germany and other nations around the world understand the dangers of the Iranian government having a nuclear weapon," said Bush.

Earlier in Washington, the State Department also refused to accept Iran's word that it had frozen all uranium enrichment work under an agreement with Britain, France and Germany, and stressed that Iran had gone back on earlier similar promises to halt such activity.

Deputy spokesman Adam Ereli said the United States would wait for a final report from International Atomic Energy Agency (IAEA) chief Mohamed ElBaradei on Iranian compliance before drawing any conclusions.

"This is a situation we've been in before, where Iran has said that it would suspend, and then subsequently went on to renege on those commitments," Ereli told reporters. "So obviously our interest is seeing not what they say, but what they actually do."

The IAEA, the UN nuclear watchdog, has a team of inspectors in Iran to verify that Tehran makes good on the agreement it reached earlier this month with Britain, France and Germany to suspend enrichment work.

ElBaradei is to present a report on Iran's compliance to the IAEA governing board when it meets in Vienna on Thursday and has said his team should be able to verify suspension by then.

The United States accuses Iran of using a civilian atomic energy program to secretly develop nuclear weapons and has been pressing for the IAEA to refer the matter to the UN Security Council for possible sanctions.

Iran vehemently denies the charges but agreed a week ago with the so-called "EU Three" to suspend as of Monday all its uranium enrichment-related activities, including making uranium gas and building centrifuges, in order to avoid the sanctions threat at the United Nations.

Earlier Monday in Tehran, Iranian government spokesman Abdollah Ramazanzadeh said Iran was freezing its controversial nuclear fuel work in line with the agreement.

Shortly afterward, ElBaradei hinted that he expected the suspension to be verified and said he thought the move was "a step in the right direction" by Tehran.

"I think pretty much everything has come to a halt right now, so we are just trying to make sure that everything has been stopped," he told reporters in Vienna. "Hopefully by Thursday I should be able to report that we've verified the suspension."

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