Yukiya Amano, chief of the International Atomic Energy Agency, made the comment during the regulatory body's board of governors meeting in Vienna several weeks after IAEA's inspectors returned from talks in Tehran after failing to secure access to the Parchin military site, about 20 miles from Iran's capital, The New York Times reported.
"I request Iran once again to provide access to the Parchin site without further delay," Amano said. "Providing access to the Parchin site would be a positive step which would help to demonstrate Iran's willingness to engage with the agency on the substance of our concerns."
Talks about Parchin access are separate from negotiations Iran is conducting with six global powers -- U.S. Security Council permanent members Britain, China, France, Russia and the United States, plus Germany -- on Iran's disputed nuclear program, which the Islamic republic maintains is for peaceful purposes. Western leaders suspect Iran is working to develop nuclear weapons technology.
The latest round of those talks ended last week in Almaty, Kazakhstan, with agreement for more meetings in March and April on a proposal that would restrict Iran's stockpile of the most dangerous enriched uranium in exchange for lifting some sanctions.
"Iran is not providing the necessary cooperation to enable us to provide credible assurance about the absence of undeclared nuclear material and activities," Amano said Monday. "The agency therefore cannot conclude that all nuclear material in Iran is in peaceful activities."
"We must not lose sight of the ultimate goal, which is to resolve all outstanding issues related to Iran's nuclear program," Amano said. "Dialogue should produce results."