Iran's President Hassan Rouhani said Tehran would begin injecting gas into centrifuges at the Fordow plant, a restriction it had originally accepted in return for lifting international sanctions.
Iran's president announced on Tuesday that Tehran would begin injecting uranium gas into 1,044 centrifuges, the latest step away from its nuclear deal with world powers since President Donald Trump withdrew from the accord more than a year ago.
The development is significant, as the centrifuges previously spun empty, without gas injection, under the landmark 2015 nuclear accord. It also increases pressure on European nations that remain in the accord, which at this point, has all but collapsed.
The suspension of all enrichment at the Fordow plant in the mountains near Qom was one of the restrictions on its nuclear activities that Iran accepted in return for the lifting of international sanctions.
In his announcement, President Hassan Rouhani did not say whether the centrifuges, which are at its nuclear facility in Fordow, would be used to produce enriched uranium. The centrifuges would be injected with the uranium gas as of Wednesday, Rouhani said.
All of the steps Iran has taken to reduce its commitments to the nuclear deal are reversible and Iran will uphold all of its commitments under the deal when the remaining signatories do the same, Rouhani said.
His remarks, carried live on Iranian state television, came a day after Tehran's nuclear program chief said the country had doubled the number of advanced IR-6 centrifuges in operation.
There was no immediate reaction from the International Atomic Energy Agency, the UN nuclear watchdog now monitoring Iran's compliance with the deal.
The EU on Monday called on Iran to return to the deal, while the White House sanctioned members of Supreme Leader Ayatollah Ali Khamenei's inner circle as part of its maximalist campaign against Tehran.
Rouhani stressed the steps taken so far, including going beyond the deal's enrichment and stockpile limitations, could be reversed if Europe offers a way for it to avoid US sanctions choking off its crude oil sales abroad.
"We should be able to sell our oil," Rouhani said. "We should be able to bring our money" into the country.
The centrifuges at Fordow are IR-1s, Iran's first-generation centrifuge. The nuclear deal allowed those at Fordow to spin without uranium gas, while allowing up to 5,060 at its Natanz facility to enrich uranium.
A centrifuge enriches uranium by rapidly spinning uranium hexafluoride gas. An IR-6 centrifuge can produce enriched uranium 10 times faster than an IR-1, Iranian officials say.
Iranian scientists also are working on a prototype called the IR-9, which works 50-times faster than the IR-1, Iran's nuclear chief Ali Akhbar Salehi said on Monday.
As of now, Iran is enriching uranium up to 4.5 percent in violation of the accord's limit of 3.67 percent.
Enriched uranium at the 3.67 percent level is enough for peaceful pursuits but is far below weapons-grade levels of 90 percent.
At the 4.5 percent level, it is enough to help power Iran's Bushehr reactor, the country's only nuclear power plant. Prior to the atomic deal, Iran only reached up to 20 percent.
Tehran has gone from producing some 450 grammes of low-enriched uranium a day to 5 kilogrammes, Salehi said. Iran now holds over 500 kilogrammes of low-enriched uranium, Salehi said. The deal had limited Iran to 300 kilogrammes.