The UN nuclear watchdog (IAEA) on Tuesday described as "unacceptable" incidents in Iran involving its inspectors, in which diplomats say security staff subjected female inspectors to inappropriate searches that the United States is calling harassment.

In a first case this year at the Natanz nuclear site, a female inspector was subjected to an unnecessarily intrusive search by security staff, diplomats who follow the International Atomic Energy Agency have said.

The Wall Street Journal, first to report on the issue, said the behavior continued over several months and the United States has circulated a paper among IAEA member states demanding that Iran stop the wrongful conduct immediately. IAEA’s Board of Governors is meeting this week.

“Harassment of IAEA inspectors is absolutely unacceptable, and we strongly urge you to make clear in your national statement at the Board meeting that such conduct is deplorable and must end immediately, and that the Board should take appropriate action if further incidents are reported,” the WSJ quoted the US paper as saying.

Details of the episode in June remain unclear as does the number of repeat incidents since at Natanz, Reuters said, where an explosion and power cut that Iran has blamed on Israel damaged machines in its main, underground uranium-enrichment plant in April.

One diplomat told WSJ that there have been at least four such harassment incidents.

"In recent months, there have been some incidents related to security checks of Agency inspectors at one Iranian facility," the IAEA said in a statement issued in response to a Wall Street Journal report on the episodes.

The IAEA, which treats details of inspections as confidential, did not specify the inspectors' gender or say what happened.

"The Agency immediately and firmly raised this issue with Iran to explain in very clear and unequivocal terms that such security-related incidents involving Agency staff are unacceptable and must not happen again," the IAEA said.

"Iran has provided explanations related to reinforced security procedures following events at one of their facilities. As a result of this exchange between the Agency and Iran there have been no further incidents."

Iran's ambassador to the IAEA, Kazem Gharibabadi, tweeted: "Security measures at the nuclear facilities in Iran are, reasonably, tightened. The IAEA inspectors have gradually come up with the new rules and regulations."

Iran’s parliament passed a law in December 2020, restricting access by IAEA inspectors but allowed work related to the Non-proliferation treaty to continue. The UN nuclear watchdog last week issued two reports criticizing Iran’s lack of cooperation, both in providing explanations about its past nuclear work and also about limits to the Agency’s monitoring work.

On September 12, IAEA’s director Rafael Grossi visited Iran and secured agreement to do maintenance work on surveillance cameras installed in nuclear facilities. The US indicated it will not pursue a resolution against Iran at the IAEA board meeting this week.

It is not the first time there have been tensions between the IAEA and Iran over access to Natanz and the treatment of female inspectors.

In 2019, Iran for the first time briefly held and confiscated the travel papers of a female inspector. Tehran later said it had been concerned she might be carrying "suspicious material".

After the apparent attack in April, Iran also restricted inspectors' access to the main, underground enrichment plant there, citing security concerns - a standoff that lasted until July.

With reporting by Reuters, WSJ