The US said today that Iran's response to a package of incentives offered by world powers "falls short" of what was demanded by a UN Security Council resolution.
In the first US response to Iran's reply to the offer, the White House said the United States was consulting closely with other Council members over what steps to take.
"We acknowledge that Iran considers its response as a serious offer and we will review it," White House spokeswoman Dana Perino said.
"The response, however, falls short of the conditions set by the Security Council which require the full and verifiable suspension of all enrichment-related and reprocessing activities."
Iran handed over its formal response on Tuesday to a nuclear incentives offer from major powers and said it contained ideas that would allow serious talks about its standoff with the West to start immediately.
But Tehran gave no sign of heeding a key United Nations Security Council demand that it freeze uranium enrichment by Aug. 31 or face the prospect of sanctions.
France said earlier that world powers were ready to take up Iran's call for talks only if it first suspends uranium enrichment.
The UN Security Council has warned Iran could face sanctions if it does not meet an August 31st deadline to freeze enrichment work, a process that can be used to make fuel for nuclear power plants or material for warheads.
The five permanent Council members - Britain, China, France, Russia and the United States - plus Germany offered Iran economic and other incentives to stop enrichment.
So far, they have not given their verdict on Iran's reply. Analysts say Iran's answer, described by diplomats as complex and nuanced, was probably designed to divide Security Council members Russia and China, both key trade partners of Tehran, from the United States, Britain and France, which have backed tougher sanctions. All five have a veto on the Council.