The officials, who spoke on condition of anonymity because of the confidentiality of the information, told The Associated Press that Iran's unprecedented refusal to allow access to the facility at Natanz could seriously hamper international efforts to ensure that Tehran is not trying to make nuclear weapons.
The revelation came on the eve of Iran's self-imposed Aug. 22 deadline to respond to a Western incentives package for it to roll back its disputed nuclear program. The United Nations has given Tehran until the end of August to suspend uranium enrichment.