State Department spokesman Adam Ereli suggested the Iranian decision reflected the extremely difficult conditions in Bam after the Dec. 26 earthquake, which killed more than 30,000 people and left tens of thousands homeless.

"We have heard back today from the Iranians that given the current situation in Bam and all that is going on there now, it would be preferable to hold such a visit in abeyance. Therefore we are not pursuing it further at the moment," Ereli said.

It was unclear whether Iran's decision not to accept the visit reflected a calculated rebuff or simply bad timing.

Ereli declined to say whether a visit by Dole, a North Carolina Republican, might take place at some point in the future and he stressed the United States would keep providing humanitarian aid to Iran.

The United States said its offer to send Dole, who has extensive experience grappling with humanitarian disasters from her stint heading the American Red Cross in the 1990s, was a humanitarian rather than a political gesture.

Washington cut ties with Tehran in 1980 after the Iranian revolution brought to power an anti-American government. The decision to sever ties was taken during the 1979-81 hostage crisis when Iranian students held 52 Americans for 444 days.