The State Department said the denial of access to the two sites, despite Tehran's repeated insistence that it is not developing nuclear arms and vows to cooperate with the IAEA, was "an anomaly in Iran's behavior."

"The issue here is Iran's commitments to transparency, Iran's commitments to openness, Iran's repeated statements that they're not seeking to develop nuclear weapons and how Iran can build confidence in the world that they're indeed sincere and true," spokesman Richard Boucher said.

"One would think that if they really wanted to demonstrate to the world that they were not developing nuclear weapons, they would have absolutely no problem at all in allowing inspections of any facility, anywhere, on any suspicion, on any grounds, because they would have nothing to hide," he told reporters.

"We expect Iran to provide prompt and unrestricted access to the International Atomic Energy Agency," Boucher said. "This is an issue where Iran needs to try to demonstrate the truth and sincerity of its statements.

"If Iran truly has nothing to hide, one would expect them not only to comply, but to do so with gusto," he said.

Earlier Thursday at IAEA headquarters in Vienna, diplomats said Iran was refusing to allow inspectors to visit the Parchin military site southeast of Tehran where there may have been nuclear weapons technology testing.

They also said the inspectors were legally restricted from checking out buildings at a location in northeast Tehran known as Lavizan-II where Iranian resistance spokesmen have said secret uranium enrichment was allegedly going on.

The IAEA on Monday spared Iran from being referred to the UN Security Council for possible sanctions after Tehran agreed, in a deal with Britain, France and Germany, to suspend its uranium enrichment program and allow inspections of its atomic sites.

But the deal refers to civilian nuclear energy production sites, not to military facilities, which are traditionally off limits to the agency.

The New York Times reported Thursday that IAEA chief Mohamed ElBaradei had asked Tehran repeatedly and unsuccessfully for access to Parchin and Lavizan-II.

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