A week after Washington called off air strikes just minutes before impact, diplomats say Iran is days away from exceeding the maximum amount of enriched uranium allowed under its 2015 nuclear deal with world powers, which Washington quit last year.

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Each step Iran takes narrows the time its leaders would need to have enough highly enriched uranium for an atomic bomb — if they chose to build one.

By Thursday, Iran said it had over 300kgs of low-enriched uranium in its possession, which would mean it had broken out of the atomic accord.

The countries that are still signed up to the agreement — European powers Britain, Germany and France plus Russia and China — held urgent talks with Iranian officials on Friday in Vienna in the hope of persuading Tehran to hold off.

The Europeans say a breach of the agreement by Iran would escalate confrontation at a time when Tehran and Washington are at risk of a miscalculation that could trigger a war.

Iran’s envoy, Deputy Foreign Minister Abbas Araqchi, said the talks were “a step forward, but it is still not enough and not meeting Iran’s expectations”.

He said it was ultimately up to his superiors in Tehran to decide whether to call off plans to exceed limits in the nuclear deal, but he did not believe the talks’ outcome was likely to change their minds.

The likelihood that Iran could exceed the deal’s limits as soon as the next few days is the next looming worry for European leaders trying to keep confrontation between Washington and Tehran from spiralling out of control.

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Despite abandoning the deal, Washington has demanded European countries ensure Iran keeps complying with it.

Iran says it cannot do so unless the Europeans provide it with some way to receive the deal’s promised economic benefits.

In particular, it wants its oil exports restored to the level of April 2018, before Trump reimposed sanctions.

French President Emmanuel Macron said this week he would ask US President Donald Trump to ease sanctions to allow negotiations to begin.

But the plea seemed to have fallen on deaf ears, with Trump’s Iran envoy saying yesterday sanctions would remain in place to end Iranian oil exports altogether.

China, long a big importer of Iranian oil, said it rejected US sanctions, but Fu Cong, director general of the Department of Arms Control of the Chinese foreign ministry, would not be drawn on whether Beijing planned to keep buying.

So far, European proposals to protect Iran from the impact of US sanctions have failed, with Iran largely shunned in international oil markets and all major companies cancelling plans to invest there for fear of falling afoul of US rules.

After Friday’s talks, Araqchi said he had been informed that INSTEX, a new barter mechanism set up by the Europeans to facilitate some trade with Iran, was now operational.

A European diplomat said it was now working on the European side and transactions had been identified, but work on the Iranian end had yet to be completed.

Araqchi said the new mechanism would help only if it enables Iran to sell its oil.

The Europeans say it is likely to be able to handle only small transactions for items such as medicine, already permitted under sanctions.