The “fluctuations” in Iran’s Natanz plant pushed to 63% the purity of uranium, higher than the 60% announced that its nuclear deal was complicated with world power, according to a United Nations nuclear watchdog report on Tuesday.

In response to an outbreak and power cuts in Natanz, which Teheran accused Israel of and seems to have damaged its energy enrichment output in a large underground plant there, Iran made the transition to 60 per cent – a big step from the previously achieved 20 per cent.

Iran’s move rattled the current indirect talks with the United States to agree conditions for both sides to return fully to the 2015 nuclear deal, which was undermined when Washington abandoned it in 2018, prompting Tehran to violate its terms.

The deal says Iran cannot enrich beyond 3.67% fissile purity, far from the 90% of weapons-grade. Iran has long denied any intention to develop nuclear weapons.

“According to Iran, fluctuations of the enrichment levels… were experienced,” the International Atomic Energy Agency (IAEA) said in the confidential report to its member states, seen by Reuters.

“The agency’s analysis of the ES (environmental samples) taken on 22 April 2021 shows an enrichment level of up to 63% U-235, which is consistent with the fluctuations of the enrichment levels (described by Iran),” it added, without saying why the fluctuations had occurred.

A previous IAEA report last month said Iran was using one cascade, or cluster, of advanced IR-6 centrifuge machines to enrich to up to 60% and feeding the tails, or depleted uranium, from that process into a cascade of IR-4 machines to enrich to up to 20%.

Tuesday’s report said the Islamic Republic was now feeding the tails from the IR-4 cascade into a cascade of 27 IR-5 and 30 IR-6s centrifuges to refine uranium to up to 5%.