"IAEA inspectors must be allowed to conduct their critical work unimpeded. We call on Iran to immediately resolve all open issues with the IAEA and to afford Agency inspectors the privileges and immunities to which they are entitled," Pompeo said in a statement.
Pompeo called the incident "an outrageous and unwarranted act of intimidation."
Iran’s undeclared nuclear materials were discussed at the recent meeting of the IAEA Board of Governors, he noted.
"Iran has no plausible explanation for the detected materials and must explain where these nuclear materials came from and where they are now," Pompeo said.
He also reiterated that the Joint Comprehensive Plan of Action (JCPOA), signed by Iran and other countries in 2015, was "both false and fraudulent."
On Wednesday, the Atomic Energy Organization of Iran (AEOI) confirmed media reports that it had prevented an IAEA inspector from examining the Natanz plant. According to the AEOI, the security equipment at the facility's entrance had shown the presence of suspicious materials among the inspector's belongings.
Iran announced the gradual reduction of its JCPOA obligations on 8 May, which marked the first anniversary of the US' unilateral pullout from the nuclear pact. Tehran then said that it would start abandoning some parts of its nuclear obligations every 60 days unless European signatories to the deal ensured Iran's interests amid Washington’s reinstated sanctions.
On 7 November, Tehran began enriching uranium at the Fordow Fuel Enrichment Plant as part of the fourth stage of reducing its obligations under the JCPOA after Washington's withdrawal.