Iran has invited a number of ambassadors accredited to the International Atomic Energy Agency in Vienna to tour its nuclear facilities - but not the United States.
No explanation was given for the invitation, but the BBC reports the visit in a fortnight would come just before Iran is due to have a fresh round of UN-sponsored talks about its nuclear programme.
The offer was reportedly extended to Russia, China and several EU countries, but not the US.
US State Department spokesman, Philip J Crowley, has dismissed the offer as a "clever ploy".
Western countries suspect Iran is developing nuclear weapons, but Tehran says the programme is peaceful.
Citing European diplomats close to the negotiations, The New York Times reports that the invitation has "pointedly snubbed" the United States.
Washington, which is spearheading the campaign for sanctions against Iran, has dismissed the offer anyway.
"It's a clever ploy, but it's not a substitute for Iran's responsibilities to the [International Atomic Energy Agency] IAEA," State Department spokesman Philip J Crowley told the New York Times.
Tehran is already subject to inspections by the IAEA, but the BBC says it appears that this tour may be aimed at diplomats, not inspectors. The last such trip which Tehran arranged was in February 2007.
Foreign Ministry spokesman Ramin Mehmanparast said the visit would take place ahead of a second round of talks on Tehran's nuclear programme, scheduled for late January in Istanbul, Turkey, although no date has been confirmed.
He did not say which nuclear facilities the envoys would travel to.
UN sanctions
The UN Security Council has imposed four rounds of sanctions on Iran and demanded that it stops its uranium enrichment programme.
Iranian negotiators have flatly ruled out discussing such demands at the meeting in Istanbul.
