By Laurence Norman

Iran has produced material that is banned under the 2015 nuclear accords and could be used to form the core of a nuclear weapon, as it seeks to step up pressure on the Biden administration to lift economic sanctions on Tehran.

A confidential report by the United Nations atomic agency, seen by The Wall Street Journal, said Iran had started producing uranium metal on Feb. 6 at a nuclear facility in Isfahan that is under the agency's inspection.

The material produced was a small amount of natural uranium metal, the International Atomic Energy Agency reported, meaning it wasn't enriched. To use uranium metal for a nuclear weapon core, Iran would need around half a kilogram, or slightly more than one pound, of highly enriched uranium metal, experts say.

The Iranian government in December warned that it could start producing uranium metal within five months, following a law passed in Iran's Parliament on Dec. 1, a threat that alarmed Western diplomats.

Iran has taken a series of recent steps in breach of the 2015 nuclear accord, from which the Trump administration withdrew. Tehran has increased its production of nuclear fuel, carried out enrichment in new sites and earlier this year produced 20% enriched uranium, the highest purity of the material it has made since 2013.

Most of these steps involve enriching uranium, an activity that has potential civilian uses such as fuel for power-generating reactors or for medical isotopes. However, the production of uranium metal is more clearly linked to nuclear-weapons work since it has few civilian purposes. Iran was banned from producing it for 15 years under the 2015 agreement.

Iran's latest breach is expected to further stoke tensions over Iran's nuclear activities as the Biden administration looks to resume diplomacy aimed at returning to the accord.

Iran has warned it will start to restrict the access of IAEA inspectors in the country on Feb. 21 unless the U.S. moves to lift sweeping sanctions Washington imposed on Tehran after former President Donald Trump pulled the U.S. out of the nuclear deal in May 2018. That would partially reverse one of the most important restraints on Iran's activities built into the nuclear deal.

European officials have been trying to explore ways to persuade Iran to delay that step and have been seeking a gesture from Washington that could persuade Tehran to back off, according to diplomats. However, people briefed on the talks say it looks increasingly unlikely that Washington will make any quick move that would persuade Iran to push back its deadline.

In recent days, President Biden said the U.S. wouldn't make the first move to persuade Iran to reverse its nuclear breaches by lifting sanctions before Tehran acted.

"The proposition that has been put on the table for some months now is quite clear: We continue to encourage Iran to resume full compliance with" the nuclear deal, State Department spokesman Ned Price said late Wednesday in response to the uranium-metal report.

Last month, the IAEA reported that Iran had told the agency it wished to make uranium metal enriched to 20% in order to produce a fuel called silicide for its research reactor in Tehran, a civilian facility. The IAEA said Iran told them in January it would take four to five months to finish installing the equipment to produce the powder from which uranium metal is made. There was no timeline for producing the uranium metal itself.

In a statement Wednesday evening, an IAEA spokesman confirmed the uranium metal production and said it was part of Iran's "stated aim to produce fuel for the Tehran" research reactor. The agency said the small amount of material produced, 3.6 grams, was part of new research work on uranium metal that Iran informed the agency about last month and that it resulted from a "laboratory experiment" at Isfahan.

In a statement last month, France, Britain and Germany, the three European powers who helped negotiate the nuclear deal, expressed deep concerns about Iran's uranium metal work. "Iran has no credible civilian use for uranium metal. The production of uranium metal has potentially grave military implications," they said.

"Iran risks overplaying its hand with this attempt to pressure the U.S. ... to deliver on sanctions relief," said Kelsey Davenport, director for nonproliferation policy at Arms Control Association, a Washington think tank. "Natural uranium isn't used for nuclear weapons, but the knowledge Iran gains from the process of producing uranium metal is relevant and can't be reversed."

Iran started taking steps in breach of the 2015 nuclear accord more than a year after the Trump administration withdrew from the deal and months after Washington imposed sanctions.

In 2019, it breached the limits on its enriched uranium stockpile and purified uranium to levels slightly above those permitted in the accord. It also started enriching uranium at Fordow, a site buried deep underground.

Last year, it significantly increased its production of enriched uranium so that in November, the IAEA reported Iran had accumulated over 12 times its permitted uranium stockpile. It also sped up its research work on producing advanced centrifuges, machines that can enrich uranium far more quickly.

As a result, Western officials have said Iran could now be just three to four months away from amassing enough fissile material for a nuclear weapon. The 2015 nuclear accord was built around keeping Tehran at least a year away from having enough enriched uranium for one weapon for at least 10 years.

The Biden administration has said that if Iran walks back its nuclear breaches, the U.S. will return to the accord before seeking a new agreement with Iran that could broaden and deepen the constraints agreed in the 2015 deal.

Critics of the accord, negotiated during the Obama administration, say that it leaves Iran able to scale up its nuclear activities after 10 years, providing a pathway to produce nuclear weapons in future. Israeli and U.S. officials have said the discovery of a nuclear archive during an Israeli raid in Tehran in 2018 and subsequent findings of undeclared nuclear material in Iran show Tehran hasn't given up its ambitions to develop nuclear weapons.

--William Mauldin contributed to this article.

Write to Laurence Norman at laurence.norman@wsj.com

(END) Dow Jones Newswires

02-10-21 1755ET