The invitation — which seemed calculated to divide the alliance of nations opposed to Iran’s nuclear ambitions before the next round of negotiations over the program — was swiftly dismissed by the United States.

“It’s a clever ploy, but it’s not a substitute for Iran’s responsibilities to the I.A.E.A.,” said the State Department spokesman, Philip J. Crowley, referring to the International Atomic Energy Agency, which has been locked in an increasingly tense standoff with the Iranian government over its enrichment of uranium…

The Associated Press, citing an unidentified diplomat, said Iran was offering access to sites at Natanz and Bushehr, as well as meetings with two top officials involved in the program: Ali Salehi, the acting foreign minister who oversees it, and Saeed Jalili, the chief nuclear negotiator.