Iran is obstructing a UN investigation into a site first identified by Prime Minister Benjamin Netanyahu last year as a secret nuclear warehouse used to store radioactive material, the Wall Street Journal reported Monday night.

Unidentified diplomats told the newspaper Iran was refusing to provide answers to questions posed by the International Atomic Energy Agency, in what was apparently the first instance of Tehran failing to cooperate with inspectors.

The diplomats said there were internal disagreements in the IAEA on how severely Iran should be censured over the issue. A recent IAEA report on Iran’s growing breach of the 2015 nuclear deal reportedly made only vague reference to Tehran’s lack of cooperation with inspectors, saying “Ongoing interactions between the Agency and Iran relating to Iran’s implementation of its Safeguards Agreement and Additional Protocol require full and timely cooperation by Iran.”

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A July report on Israel’s Channel 13 claimed inspectors had visited the site several times after Netanyahu identified it in an address to the UN General Assembly last September, took soil samples, and had since definitively concluded that there were “traces of radioactive material” there.

The diplomats told the WSJ that the 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 disbelieve 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.

Speaking at the United Nations last September, Netanyahu called on the IAEA to inspect what he said was the “secret atomic warehouse” in the Iranian capital.

He claimed some 15 kilograms (33 pounds) of radioactive material had been recently removed from the atomic warehouse and squirreled away around Tehran, endangering the capital’s residents. The site may have contained as much as 300 tons of nuclear-related equipment and material in 15 shipping containers, Netanyahu added. He did not specify what nuclear material was contained at the site.

That speech came months after Israel’s disclosure that it had spirited away what it said was a “half-ton” of Iranian nuclear documents from Tehran, with Netanyahu saying both the archive and the warehouse were proof that Iran continues to seek atomic weapons despite the 2015 international agreement to limit its nuclear program. “Iran has not abandoned its goal to develop nuclear weapons…. Rest assured that will not happen. What Iran hides, Israel will find,” Netanyahu told the UN.

Following Netanyahu’s UN appearance, the late IAEA head Yukiya Amano said at the time that nuclear inspectors had visited “all the sites and locations in Iran which it needed to visit,” while pushing back against the prime minister’s assertion that the organization had failed to act on intelligence provided by Israel on the warehouse.

Diplomats quoted in April, however, said the IAEA later visited the site in Tehran’s Turquzabad district multiple times.

Referring to Netanyahu’s statements as “ridiculous,” an Iranian state TV report said the country was committed to nonproliferation and noted Iran’s nuclear program was under surveillance of the IAEA. A state TV website briefly reported the Netanyahu accusation and called it an “illusion.”

A Tasnim News reporter who visited the warehouse last October was told by a worker from inside the facility that it was not a military site, and that the Israeli leader was “a stupid person” for believing it was a nuclear warehouse. The reporter did not enter the facility, only speaking to the worker via intercom from outside the locked gate.

Also Monday an Iranian government spokesperson warned Tehran would “take a strong step” away from its 2015 nuclear deal with world powers if Europe cannot offer the country new terms by a deadline at the end of this week, as top Iranian diplomats traveled to France and Russia for last-minute talks.

The comments from Ali Rabiei reinforced the deadline Iran had set for Friday for Europe to offer it a way to sell its crude oil on the global market. Crushing US sanctions imposed after US President Donald Trump withdrew America from the deal over a year ago have halted those sales.

The IAEA report last week said Iran’s stockpile of low-enriched uranium still exceeds the amount allowed by the so-called Joint Comprehensive Plan of Action, or JCPOA as the deal is known.

The UN agency also said Iran continues to enrich uranium up to 4.5%, above the 3.67% allowed.

Enriched uranium at the 3.67% level is enough for peaceful pursuits and is far below weapons-grade levels of 90%. At the 4.5% level, the uranium can help power Iran’s Bushehr reactor, the country’s only nuclear power plant.

It remains unclear what further step Iran will take, though it could involve restarting advanced centrifuges prohibited by the deal or further bumping up its enrichment of uranium. Iran insists the steps it has taken so far are easily reversible.

Rabiei also claimed Monday that Iran’s views have been converging with those of France on ways to save the nuclear deal.

He suggested President Hassan Rouhani could meet US counterpart Donald Trump if it served Iran’s interests, while cautioning there was no need to meet an “agitator” in the current circumstances.

Rouhani has had a series of phone calls with French President Emmanuel Macron in recent weeks aimed at salvaging the 2015 nuclear deal.

The French leader has been trying to convince the United States to offer Iran some sort of relief from sanctions it has imposed on the Islamic republic since pulling out of the deal in May last year.

“In the past few weeks, there have been serious negotiations” between Rouhani and Macron, as well as talks with other European nations, said Rabiei.

“Fortunately, in many areas, our views have come closer together,” the government spokesman told a news conference.

Agencies contributed to this report.