A view of the Natanz uranium enrichment facility 250 km (155 miles) south of the Iranian capital Tehran, March 30, 2005. REUTERS/Raheb Homavandi/File Photo

Iran has deepened a key breach of its 2015 nuclear deal, enriching uranium with a larger number of advanced centrifuge machines in an underground plant as it faces off with the new US administration on salvaging the accord.

Tehran has recently accelerated its breaches of the deal, raising pressure on US President Joe Biden as both sides say they are willing to come back into compliance with the badly eroded agreement if the other side moves first.

Iran began its breaches in 2019 in response to Washington’s withdrawal in 2018 under then-President Donald Trump and the reimposition of US economic sanctions against Tehran that were lifted under the deal.

The accord says Iran can refine uranium only at its main enrichment site — an underground plant at Natanz — with first-generation IR-1 centrifuges. Last year Iran began enriching there with a cascade, or cluster, of much more efficient IR-2m machines and said in December it would install three more.

“Iran has completed the installation of one of these three cascades, containing 174 IR-2m centrifuges, and, on 30 January 2021, Iran began feeding the cascade with UF6,” the International Atomic Energy Agency said in a report obtained by Reuters on Tuesday, referring to uranium hexafluoride feedstock.

The IAEA later confirmed that the Islamic Republic had started enriching with the second cascade.

Tehran is also pressing ahead with the installation of more advanced centrifuges, the report indicated. Of the remaining two cascades of IR-2m machines, installation of one had begun while the other’s installation was “nearing completion,” it said.

Iran‘s ambassador to the IAEA, Kazem Gharibabadi, said on Twitter Tehran had also started installing IR-6 centrifuges at Fordow, a site dug into a mountain where Iran has begun enriching uranium to the 20% purity it last achieved before the 2015 deal.

In a second report on Tuesday evening also reviewed by Reuters, the IAEA said only that Iran had informed it in a letter dated Feb. 1 that two cascades of IR-6 centrifuges would be installed at Fordow to be used with the 1,044 IR-1 machines already enriching in six cascades there.

The report did not say installation had begun.

The IAEA confirmed in a statement that Iran had informed it that the two cascades would be installed at Fordow.

Earlier on Tuesday Israel’s energy minister said it would now take Iran about six months to produce enough fissile material for one nuclear weapon, a timeline almost twice as long as that anticipated by a senior Biden administration official.

Iran denies any intent to produce nuclear weapons. The nuclear deal sets a limit of 3.67% enrichment purity, suitable for producing civilian nuclear energy and far below the 90% that is weapons-grade.