Iran is “dramatically” increasing the amount of uranium enriched to up to 60 per cent purity, close to the roughly 90pc of weapons-grade uranium that it can produce, the watchdog’s chief Rafael Grossi told Reuters in an interview.

The move is certain to cause even greater alarm in Western capitals already arguing that there is no civil justification for Iran’s enrichment to that level as no other country has done so without producing nuclear bombs, which Iran denies pursuing.

Iran already has enough material enriched to up to 60pc, its most highly enriched stock, for four nuclear weapons in principle if it enriched it further, according to an International Atomic Energy Agency (IAEA) yardstick. It has enough for more at lower enrichment levels.

“Today the agency is announcing that the production capacity is increasing dramatically of the 60pc inventory,” IAEA chief Grossi said on the sidelines of the Manama Dialogue security conference in Bahrain’s capital.

He added that it was set to rise to “seven, eight times more, maybe, or even more” than the previous rate of 5-7 kilogrammes a month.

The move is also a setback for Grossi since he said after a trip to Iran last month that Tehran had accepted his “request” to cap its stock of uranium enriched to up to 60pc to ease diplomatic tensions, calling it “a concrete step in the right direction”.

Diplomats said at the time, however, that Iran’s step, which included preparing to implement that cap, was conditional on the IAEA’s 35-nation Board of Governors not passing a resolution against Iran over its insufficient cooperation with the agency, which the Board then did regardless.