The flag of the International Atomic Energy Agency (IAEA) flies in front of its headquarters in Vienna, Austria.

Several nuclear security experts are urging the United Nations nuclear watchdog and world powers to release details of how a sensitive Iranian military site will be inspected as part of a landmark nuclear deal reached in July.

The experts, with long experience in international weapons inspections, said the failure to disclose the details was damaging the credibility of the International Atomic Energy Agency (IAEA), a view that is rejected by the agency itself, the United States government and another prominent non-proliferation expert.

The confidential plan for the Parchin site has led to differing reports on how it will be carried out, with some critics of the U.S. administration saying Iran had been given too much leeway to conduct its own inspections, including taking samples.

The inspections are needed to resolve questions about whether Iran did research in the past at Parchin related to building a nuclear weapon.

David Albright, head of the Institute for Science and International Security in Washington, expressed unease about the lack of public details on the arrangement.

“(Details) should be released because it’s undermining the IAEA’s credibility,” Albright said. “Whatever the outcome of the sampling, the secrecy makes it harder to determine whether it’s a credible sampling approach.”

The IAEA has said it has a legal obligation to keep details of the arrangement confidential, but insists it is technically sound and will ensure the samples are not compromised.

Iranian officials have also said that international experts would not be allowed in.

Four diplomats familiar with the deal told Reuters that U.N. inspectors would be present at Parchin to oversee the inspections. In the unusual arrangement struck in July, the samples would be taken by Iranian technicians while IAEA experts present at Parchin observe and oversee the process, Western diplomats told Reuters.

The diplomats, who have knowledge of the deal, said that while the IAEA inspectors will not be next to the Iranian technicians when they take samples, they will be at Parchin overseeing the process. Cameras will record the process.

Iran cannot receive sanctions relief promised under the nuclear deal until the IAEA is satisfied it has answered outstanding questions about the so-called “possible military dimensions” of past Iranian nuclear research. Tehran says its nuclear program is peaceful and that it did not conduct atomic weapons research.