Iran will begin injecting uranium gas into centrifuges at its Fordow nuclear facility as early as tomorrow, the country's president has said.
In a televised statement on Tuesday, Iranian President Hassan Rouhani said the gas will be injected into 1,044 of its centrifuges at the plant, counter to stipulations in the 2015 nuclear treaty.
But these steps can be reversed, he added, as long as other signatories to the international agreement uphold their commitments.
"We know their sensitivity with regard to Fordow," Rouhani said. "With regards to these centrifuges, we know.
"But at the same time, when they uphold their commitments, we will cut off the gas again...So it is possible to reverse this step.
"We can't unilaterally accept that we completely fulfil our commitments and they don't follow up on their commitments."
Russia and France, both signatories on the 2015 deal, have since expressed concern over the latest action.
In a statement, the French foreign ministry spokeswoman said it was waiting for a report from the International Atomic Energy Agency (IAEA).
She added that France was still committed to the deal and encouraged Iran to "fully adhere to its obligations and to cooperate fully with the IAEA, both in [the deal] and its other nuclear obligations."
Rouhani's comments on Tuesday came just a day after Iran's nuclear chief Ali Akbar Salehi announced another accelaration of uranium enrichment with the launch of 30 advanced IR-6 centrifuges.
In his speech on the launch, Salehi appeared to attribute the decision to the US, which pulled out of the nuclear deal last year, and later imposed a series of crippling sanctions on Iran.
"We have to thank our enemies for creating an opportunity for the Islamic Republic of Iran, especially in the nuclear technology industry, to show how we could obtain such an achievement...in such a short time," he said.
Meanwhile, the US has said it plans to impose further sanctions on nine people connected to Iran's Supreme Leader Ali Khameni to "block funds from flowing to a shadow network."
In a statement, the US treasury department said: "This action seeks to block funds from flowing to a shadow network of Ali Khamenei’s military and foreign affairs advisors who have for decades oppressed the Iranian people, exported terrorism, and advanced destabilising policies around the world."