(Bloomberg) -- International atomic monitors in Iran have detected uranium enriched to levels just below nuclear weapons-grade, risking an escalation over Tehran’s expanding program.  

The International Atomic Energy Agency is trying to clarify how Iran accumulated uranium enriched to 84% purity — the highest level found by inspectors in the country to date, and a concentration just 6% below what’s needed for a weapon. 

Iran says its decades-long atomic program is for peaceful purposes but Western powers and Israel have accused it of working toward a nuclear bomb. Building a bomb would require further technical steps which have so far not been detected by the IAEA and a political decision to go ahead. 

The development was reported by Bloomberg on Sunday, citing two senior diplomats. Iran had previously told the IAEA that its centrifuges were configured to enrich uranium to a 60% level of purity. 

US Secretary of State Antony Blinken said he had seen the report and is in close contact with the IAEA and European countries about the matter, adding he’ll have more to say when he has more information, according to comments made to reporters in the Turkish capital, Ankara, on Monday. 

The development comes as Iran is increasingly isolated from the West, nuclear talks with world powers are suspended and regional tensions have sharpened. Israel has blamed Iran for a Feb. 10 attack on an oil tanker in the Arabian Sea, that Iran has denied. It came about a fortnight after a drone strike on a weapons depot near Iran’s city of Isfahan that Tehran blamed on Israel, the latest incident in a string of suspected tit-for-tat attacks. 

Iran has also faced widespread condemnation for its deadly crackdown on major protests and the US and European Union have tightened sanctions on Iran over its military support for Russia’s war on Ukraine.

Inspectors need to determine whether Iran intentionally produced the material, or whether the concentration was an unintended accumulation within the network of pipes connecting the hundreds of fast-spinning centrifuges used to separate the isotopes. It’s the second time this month that monitors have detected suspicious enrichment-related activities.

In an interview on Jan. 23 the US’s envoy for Iran, Robert Malley, said Tehran was “only a handful of weeks away from having enough weapons grade uranium” but taking the further step of developing an actual weapon is “a different matter” and so far the US had no evidence of it. 

Malley on Iran Oil Exports, Nuclear Talks (Video)

Iran’s foreign ministry spokesman said the claims show the United Nations’ atomic agency is “distancing itself from its professional conduct” and that Iran was committed to its agreements with the body and the terms of the nuclear non-proliferation treaty. 

Nasser Kanaani told reporters on Monday that plans are still afoot to organize a forthcoming visit to Tehran by the IAEA’s Director General, Rafael Mariano Grossi.  

On Sunday an Iranian nuclear official denied Iran had enriched uranium beyond 60% purity “so far” and dismissed the development as “a smear and a distortion of the facts.”

“The existence of uranium particles above 60% does not mean the same thing as enrichment above 60%,” Behrouz Kamalvandi, spokesman for the Atomic Energy Organization of Iran told the state-run Islamic Republic News Agency.  

The IAEA responded on Sunday and said it is discussing with Iran the results of the agency’s recent verification activities and will inform its board of directors as appropriate, according to a tweet citing Grossi.  

The IAEA is preparing its quarterly Iran safeguards report ahead of a March 6 Board of Governors meeting in Vienna, where the Persian Gulf nation’s nuclear work will figure prominently on the agenda. 

Iran hasn’t submitted the required forms declaring its intention to raise uranium enrichment levels at two facilities near the towns of Natanz and Fordow, according to one diplomat. 

Even if the detected material was mistakenly accumulated because of technical difficulties in operating the centrifuge cascades — something that has happened before — it underscores the danger of Iran’s decision to produce highly enriched uranium, the other diplomat said. 

The IAEA has repeatedly said levels even at just 60% are technically indistinguishable from the level needed for a nuclear weapon. Most nuclear power reactors use material enriched to 5% purity. 

A nuclear deal between Iran and world powers unraveled after then-President Donald Trump withdrew the US in 2018 and reimposed sanctions. In response, Iranian officials expanded the country’s nuclear program. Tehran denies it’s seeking to build atomic warheads but concerns it might develop the technology to do so propelled years of diplomacy that led to the deal with world powers. 

Grossi called the atomic deal an “empty shell” last month and said Iran has sufficient nuclear material for several weapons, should it make the political decision to move forward. 

--With assistance from Patrick Sykes and Arsalan Shahla.

(Updates with reaction from US in third paragraph and more comments from Iranian official.)

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