Advanced centrifuges at Iran’s Natanz facility were accumulating, or had been prepared to accumulate, enriched uranium.

VIENNA, Austria (AFP) — Iran has started using advanced models of centrifuges to enrich uranium, the United Nation’s nuclear watchdog said Thursday, in a new breach of the faltering 2015 deal with world powers.

Advanced centrifuges at Iran’s Natanz facility “were accumulating, or had been prepared to accumulate, enriched uranium,” the International Atomic Energy Agency said in a report seen by AFP.

The centrifuges concerned are 20 IR-4 centrifuges and a further two “cascades” of 30 IR-6 centrifuges, the report said.

Enriched uranium is needed to produce nuclear fuel, but higher levels of enrichment can also be used to make the fissile core of an atomic bomb.

Iran has always insisted that its nuclear program is peaceful.

In order to multiply the effects of the enrichment of a single machine, large numbers of centrifuges are interconnected to form cascades.

The IAEA report said that Iran was also pressing ahead with previously reported plans to install further cascades of advanced centrifuges.

Under the 2015 deal with world powers that puts curbs on Iran’s nuclear program in exchange for sanctions relief, Tehran is only meant to enrich uranium using less efficient IR-1 centrifuges.

The IR-4 and IR-6 models can produce enriched uranium much faster than the IR-1 models.

The landmark accord, known as the Joint Comprehensive Plan of Action, has been in jeopardy since May last year when President Donald Trump withdrew the US from it and reimposed sanctions.

The remaining parties to the deal with Iran — Britain, China, France, Germany and Russia — have tried to salvage the accord.

But Tehran has repeatedly accused Europe of not doing enough, leaving it little option but to scale back its commitments under the JCPOA.

A senior diplomat in Vienna, where the IAEA is based, said that the latest change “will increase (Iran’s) rate of accumulation” of uranium but cautioned that “it’s a small number of centrifuges in small cascades.”

The machines in question “are not run for production continuously,” the source said.

The diplomat added that there had been “no change” in Iran’s level of cooperation with the IAEA, and that the agency continued “to receive access to all the sites” it needed to visit.

Iran has already broken the limits on uranium enrichment levels and the overall stockpile of enriched uranium laid down in the JCPOA.