ISTANBUL — Iran will begin injecting gas into centrifuges at its Fordow uranium-enrichment facility in its latest step away from the 2015 nuclear accord it struck with world powers, President Hassan Rouhani said Tuesday.

In a televised address, Rouhani said the Atomic Energy Organization of Iran would begin the new measures Wednesday, feeding gas to more than 1,000 centrifuges installed at the plant.

Iran’s envoy to the Vienna-based International Atomic Energy Agency (IAEA) later announced that a letter has been sent to inform the United Nations nuclear watchdog that uranium hexafluoride gas would be injected into centrifuges at Fordow, starting the process usually used to produce enriched uranium.

Under the nuclear agreement, Iran is allowed to maintain 1,044 empty IR-1 centrifuges at Fordow and is banned from enriching uranium or even bringing uranium to the site for 15 years from the start of the accord. The site was revealed as a covert enrichment facility by Britain, France and the United States in 2009. It was constructed deep inside a mountain near the city of Qom.

It was unclear Tuesday whether Iran would begin enriching uranium at the site. But experts said the measures announced by Rouhani marked a significant escalation in Iran’s simmering confrontation with the West.

“We know how sensitive they are to the Fordow facility,” Rouhani said in his address, referring to Western powers that negotiated the 2015 deal.

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But, he said, “when they begin living up to their commitments [under the agreement], then we will stop feeding gas to the centrifuges.”

He added that the IAEA would be allowed to monitor the new activities.

Iran has taken several steps this year to reduce its nuclear obligations under the pact, which curbed Iran’s atomic energy program in exchange for widespread sanctions relief. The landmark accord was negotiated between Iran and world powers, including the United States under President Barack Obama.

President Trump, however, withdrew the United States from the agreement last year, reimposing a near-total trade embargo on the Iranian economy. The economic restrictions are part of what the administration has called a “maximum-pressure campaign” against Iran to force it to renegotiate restraints on its nuclear activities, as well as its support for proxy forces in the region and ballistic missile construction.

Instead, Iran in recent months has exceeded caps on the size and purity of its enriched uranium stockpile and doubled the number of its advanced centrifuges.

“We have made clear that Iran’s expansion of uranium-enrichment activities in defiance of key nuclear commitments is a big step in the wrong direction, and underscores the continuing challenge Iran poses to international peace and security,” State Department spokeswoman Morgan Ortagus said in an emailed statement Tuesday.

“Iran has no credible reason to expand its uranium-enrichment program, at the Fordow facility or elsewhere, other than a clear attempt at nuclear extortion that will only deepen its political and economic isolation,” the statement said.

Iranian officials have said that the moves are part of a bid to persuade European nations to offset the effects of U.S. sanctions. Iran has given Europe a series of 60-day deadlines to reset the terms of the deal, including facilitating the sale of Iranian oil, which is blocked under the U.S. embargo.

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“We should be able to sell our oil, we should be able to make banking transactions, and all sanctions on other sectors should be lifted,” Rouhani said Tuesday. “Then we will return to our previous commitments.”

Despite the recent moves, Iran continues to enrich uranium far below the 90 percent level needed to produce a nuclear weapon, according to the IAEA. In its latest report, in September, the agency said Iran was enriching uranium at 4.5 percent, slightly above the 3.67 percent cap established under the nuclear agreement.

In June, the agency reported that Iran had not conducted any uranium or related research at the Fordow plant.

“There has not been any nuclear material at the plant,” the report said.

Carol Morello in Washington contributed to this report.

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