Iran is to start injecting uranium gas into centrifuges at its underground Fordow enrichment facility, President Hassan Rouhani has said, a highly symbolic breach of the landmark international nuclear deal.
Under the 2015 agreement between Iran and world powers including the UK and US, Iran agreed to turn Fordow into a "nuclear, physics and technology centre" where 1,044 centrifuges are used for purposes other than enrichment, such as producing stable isotopes, which have a variety of civil uses.
Iran has gradually scaled back its commitments to the deal, under which it curbed its nuclear programme in exchange for the removal of most international sanctions, after the United States reneged on the agreement and reimposed sanctions.
The pact allows Iran only to spin the centrifuges at Fordow, located inside a mountain near the Shi'ite holy city of Qom, without injecting gas. Uranium gas injection could allow production of enriched uranium, banned at the facility under the pact.
"Starting from Wednesday, gas will be injected into centrifuges at Fordow as part of part of our fourth step to reduce our nuclear commitments to the deal," Mr Rouhani said in a televised speech.
He did not specify what kind of gas would be injected into centrifuges at Fordow. But Kazem Gharibabadi, Iran's ambassador to the International Atomic Energy Agency (IAEA), said Iran had informed the agency of "the start of injecting UF6 (uranium hexafluoride) into centrifuges at Fordow on Wednesday".
The deal bans nuclear material from Fordow and by injecting UF6 into centrifuges, the facility will become an active nuclear site rather than a research plant as permitted under the pact.
"The IAEA was requested to send its inspectors to monitor the process," Mr Gharibabadi said, quoted by state television. The IAEA monitors Tehran's compliance with the deal.
The measure will further complicate the chances of saving the accord, which European powers have called on Iran to respect.
UK Foreign minister Dominic Raab said after the announcement that Iran's decision posed a threat to Britain's national security.
"Iran's latest actions clearly contravene the deal and pose a risk to our national security," Mr Raab said.
"We want to find a way forward through constructive international dialogue but Iran needs to stand by the commitments it made and urgently return to full compliance."
French foreign ministry spokeswoman Agnes von der Muhll agreed, sayng:"The announcement by Iran... to increase its enrichment capacity goes against the Vienna agreement, which strictly limits activities in this area,"
Iran said on Monday it had accelerated enrichment by doubling the number of advanced IR-6 centrifuges in operation, adding that it was working on "a prototype called the IR-9, which works 50-times faster than the IR-1 centrifuges".
"The deal has become a no man's land. We're controlling less and less as it crumbles around us," a senior European diplomat said. "In terms of credibility it becomes harder and harder to not react."
Mr Rouhani gave another two-month deadline to Britain, France and Germany to salvage the deal by protecting Iran's economy from crippling US sanctions reimposed in May after Washington's withdrawal from the deal.
"We can't unilaterally accept that we completely fulfil our commitments and they don't follow up on their commitments," Mr Rouhani said.
Tehran says talks are possible if Washington lifts sanctions and returns to the deal.
"All these measures are reversible if other parties fulfil their commitments ... We should be able to sell our oil and to transfer its money into the country," Mr Rouhani said, referring to Washington's sanctions on Iran's oil and banking sectors.
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