The U.N. nuclear watchdog 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.

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

"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, said on Twitter: "Security measures at the nuclear facilities in Iran are, reasonably, tightened. The IAEA inspectors have gradually come up with the new rules and regulations."

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. 

"IAEA inspectors continue to experience inappropriate harassment from Iranian security officials at nuclear facilities," the United States said in a position paper to other countries on the IAEA Board of Governors meeting this week.

That paper, seen by Reuters, added: "Harassment of IAEA inspectors is absolutely unacceptable."

Reuters