Iran has unplugged banks of centrifuges involved in its most sensitive uranium enrichment work, prompting the United States and European Union to partially lift economic sanctions.
It puts into effect a landmark deal aimed at easing concerns over Iran’s nuclear programme.
It also starts a six-month clock for Tehran and the world powers to negotiate a final accord that the US administration and its European allies say will be intended to ensure Iran cannot build a nuclear weapon.
In the meantime, the interim deal limits Iran’s programme, though it continues low levels of uranium enrichment. Tehran says its nuclear efforts are not intended to produce a bomb.
The payoff for Iran is an injection of billions of dollars into its crippled economy over the next six months from the suspension of some sanctions, though other sanctions remain in place.
Foreign Secretary William Hague called the deal “an important milestone” but not the ultimate goal. “It’s important that other sanctions are maintained and the pressure is maintained for a comprehensive and final settlement on the Iranian nuclear issue,” he said.
European foreign ministers aim to start negotiations on a final deal next month, though no date or venue has been set. Iranian foreign minister Mohammad Javad Zarif said on Saturday that Tehran was ready to enter talks as soon as the interim deal went into force.
In the first step of the interim accord, Iranian state TV said the authorities had disconnected cascades of centrifuges producing 20 per cent enriched uranium at the Natanz plant in central Iran. It said international inspectors witnessed the stoppage before leaving to monitor suspension of enrichment at Fordo, another site in central Iran.
Iran also started to convert part of its stockpile of 20 per cent enriched uranium to oxide, which can be used to produce nuclear fuel but is difficult to reconvert for weapons use, the official IRNA news agency said.
After receiving independent confirmation of the steps from UN watchdog the International Atomic Energy Agency, EU foreign ministers approved the partial sanctions suspension.
The US also announced the suspension of some sanctions.
White House press secretary Jay Carney said: “These actions represent the first time in nearly a decade that Iran has verifiably enacted measures to halt progress on its nuclear programme, and roll it back in key respects.”
He said Iran was providing UN inspectors with increased transparency, including more frequent and intrusive inspections. “Taken together, these concrete actions represent an important step forward,” he said.
Under the deal reached in November in Geneva, Iran agreed to halt its 20 per cent enrichment programme but continue enrichment up to 5 per cent.
Iranian vice-president Ali Akbar Salehi said his country had a total of 196 kilograms of 20 per cent enriched uranium and would convert half of it to oxide over a period of six months. The remaining half will be diluted to a level below 5 per cent level within three months.
Uranium enriched to a high degree – above 90 per cent –can be used to build a nuclear warhead. Enriched below 5 per cent, it can power an electricity-generating reactor, and at 20 per cent it can power reactors used to produce medical isotopes. The enrichment is done by spinning the uranium in a series of centrifuges.
Iran will also refrain from commissioning its under-construction 40 megawatt heavy water reactor in Arak, central Iran. It can produce plutonium, another route to building a warhead.
Under the deal, the number of IAEA inspectors in Iran will “roughly double” to a maximum of eight at a time.