A former senior official at the UN nuclear watchdog said diplomats working with the atomic agency doubt Iran’s explanations for the presence of uranium at a Tehran facility that was flagged by Israel.

Olli Heinonen, ex-deputy director general of the International Atomic Energy Agency, told VOA Persian in an interview Thursday diplomats informed him that a report discussed by the organization had confirmed uranium particles were found at the Turquzabad site in Iran’s capital.

Quoting the diplomats, Heinonen said the Iranians told the UN watchdog that the particles were from junked equipment used at the Gchine uranium mine in southern Iran, which produces yellowcake. According to Heinonen, the diplomats dismissed Iran’s explanation of why the uranium was in the warehouse.

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“The diplomats told me the IAEA Secretariat described the particles as having been converted from raw uranium without specifying their exact chemical form,” said Heinonen, now an analyst at the Foundation for Defense of Democracies think tank. “They said these particles were not from yellowcake but from something more refined.”

Yellowcake is a uranium concentrate in powder form and an early step in uranium processing. It is produced by mining uranium ore from rocks and separating the uranium from the rocks by bathing them in acid. The yellowcake can then be converted, enriched to raise its purity, and then used for weapons or energy production.

Heinonen said the diplomats he spoke with were from numerous countries, none of which was Israel.

In a speech last year at the UN General Assembly, Prime Minister Benjamin Netanyahu revealed the existence of the warehouse in Turquzabad, which he said held “massive amounts” of equipment and material that were part of a secret Iranian nuclear program.

Netanyahu called for the IAEA to inspect the facility and, in July, Israeli television reported that soil samples from the warehouse turned up “traces of radioactive material,” without specifying the type.

On Sunday, Iran slammed reports that the IAEA found traces of uranium at Turquzabad.

“The Zionist regime and Israel are attempting to re-open … this file,” Iranian Foreign Ministry spokesman Abbas Mousavi was quoted by Reuters as saying Sunday on state television.

A week ago, Bloomberg reported a senior IAEA official told diplomats in a closed-door meeting in Vienna that the Islamic Republic was “evading attempts to discover the source of manmade and natural uranium particles detected at a warehouse in Tehran.”

The extraordinary meeting of the board of governors was convened by Cornel Feruta, the organization’s acting head, to discuss the latest concerns about Iran’s nuclear program, the report said.

“The IAEA has confirmed that Iran has been violating the Non-Proliferation Treaty,” Netanyahu said following the Bloomberg report. “Iran continues to hide its secret nuclear weapons program.”

In September, the Wall Street Journal reported that Iran was obstructing the investigation into the Tehran site identified by Netanyahu. Unidentified diplomats told the newspaper Iran was refusing to provide answers to questions posed by the IAEA, in what was apparently the first instance of Tehran failing to cooperate with inspectors.

The diplomats told the WSJ that the uranium traces were likely remains from Iran’s past experimentation in nuclear weapons development. Iran has denied ever seeking nuclear weapons, though Israeli and Western intelligence strongly dispute those assertions. The diplomats said the material’s existence at the site was unlikely to indicate new work on weapons development, but would be a breach of Iran’s commitment to non-proliferation.

Iran has denied that the site was a nuclear facility or served any secretive purpose. In an initial response to Netanyahu’s UN speech, Iranian state media claimed the warehouse was actually a recycling facility for scrap metal.

US President Donald Trump pulled out of the nuclear accord last year and reimposed stringent sanctions on Iran. Tehran has subsequently taken a number of steps to roll back its commitment to the accord over what it says is a failure by the deal’s remaining signatories to provide economic relief from the sanctions.

Earlier this month, Iran began injecting centrifuges with uranium at the Fordo facility, where it was barred from conducting such work under the nuclear deal.

Agencies contributed to this report.