PARIS - France, Germany and Britain said on Monday they were alarmed by an Iranian announcement that it intended to install additional, advanced uranium-enriching centrifuges and by legislation that could expand its nuclear programme.

“If Iran is serious about preserving a space for diplomacy, it must not implement these steps,” the three powers, who along with China and Russia are party to a 2015 nuclear containment deal with Tehran, known as the JCPOA, said in a joint statement.

Iran’s nuclear deal with major powers says Tehran can only use first-generation IR-1 centrifuges, which refine uranium much more slowly

A confidential International Atomic Energy Agency report obtained by Reuters said Iran plans to install three more cascades, or clusters, of advanced IR-2m centrifuges in its enrichment plant at Natanz, which was built underground apparently to withstand any aerial bombardment.

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Iran’s nuclear deal with major powers says Tehran can only use first-generation IR-1 centrifuges, which refine uranium much more slowly, at Natanz and that those are the only machines with which Iran may accumulate enriched stocks.

“Iran’s recent announcement to the IAEA that it intends to install an additional three cascades of advanced centrifuges at the Fuel Enrichment Plant in Natanz is contrary to the JCPOA and deeply worrying,” the three powers said of the UN watchdog report, which has yet to be made public.

The powers further said a new law obliging Iran’s government to halt UN inspections of its nuclear sites and step up enrichment beyond the deal’s limits was also incompatible with the accord and Iran’s wider non-proliferation commitments.

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“Such a move would jeopardise our shared efforts to preserve the JCPOA and also risks compromising the important opportunity for a return to diplomacy with the incoming US administration,” they said, referring to Joe Biden, who defeated President Donald Trump in the Nov. 3 election.

“A return to the JCPOA would also be beneficial for Iran,” the three added, referring to Tehran’s decisions to reverse some of its nuclear commitments in response to the Trump administration’s 2018 pull-out from the deal and reimposition of tough sanctions that have crippled the Iranian economy.