The US has expressed scepticism over an offer by Iran to hold talk on Iraq.
Officials say they are concerned the offer may be an attempt to divert pressure over Iran's nuclear programme.
The move by Tehran comes days before the UN Security Council meets to discuss the matter.
The US, Britain and France say members of the security council are now very close to agreement on a statement about Tehran's nuclear ambitions.
Britain and France have drawn up a text calling on Iran to suspend all nuclear enrichment and reprocessing activities.
They also want the UN agency, the IAEA, to report to the Security Council on whether Iran has complied with the demands.
