Britain, France and Germany have warned Iran against any further breaches of the international nuclear deal signed in 2015, the BBC has learnt.
In New York on Thursday, the three EU signatories to the deal said they would trigger a special dispute mechanism if there were further violations.
Iran began breaching its commitments under the deal after the US abandoned it and imposed sanctions last year.
The UN nuclear watchdog has said Iran is using banned enrichment technology.
The warning was issued at a meeting with Iranian ministers on the fringes of the UN General Assembly, reports the BBC’s James Landale at the UN General Assembly in New York.
If the dispute mechanism is triggered, the entire nuclear agreement could collapse and the UN could reinstate sanctions on Iran, which would be applied by all UN member states.
This would have a devastating impact on the Iranian economy, our correspondent says.
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The deal was first signed in 2015 by the three EU countries, as well as the US, Russia and China.
Although the agreement allowed Iran to accumulate small amounts of uranium for research, it banned the enrichment of uranium, which is used to make reactor fuel but also nuclear weapons.
Iran was also required to redesign a heavy-water reactor being built, whose spent fuel would contain plutonium suitable for a bomb, and to allow international inspections.
In May 2018 President Donald Trump abandoned the deal and reinstated US sanctions.
When the sanctions were tightened in May this year, Iran stopped abiding by some commitments in the deal.
In a report seen by Reuters news agency on Thursday, the International Atomic Energy Agency (IAEA) said: “On 25 September 2019, the Agency verified that all of the (centrifuge) cascades already installed in R&D lines 2 and 3… were accumulating, or had been been prepared to accumulate, enriched uranium.”
Iran denies ever seeking a nuclear weapons capability.
Earlier this week, French President Emmanuel Macron attempted to broker a meeting between Iranian President Hassan Rouhani and President Trump.
But Mr Rouhani told delegates at the UN that he refused to meet Mr Trump while punishing US economic sanctions were in place.
“How can someone believe them when the silent killing of a great nation, and pressure on the lives of 83 million Iranians… are welcomed by American government officials?” he said.
Iran nuclear deal: EU nations warn Tehran over breaches}