Iran began dismantling the U.N. monitoring system of its nuclear program this week, partly blinding nuclear inspectors in apparent retaliation for a resolution condemning its lack of cooperation with international inspectors, just at a moment when Tehran is again on the verge of possessing enough fuel for a bomb.
The decision by Iran’s leadership — along with a threat to install new equipment that would dramatically increase its ability to produce nuclear fuel — marks the most vivid confrontation between Iran and the West since President Donald J. Trump pulled out of the 2015 Iran nuclear agreement. Administration officials believe the chances now that the deal will be revived — a major foreign policy initiative for President Biden — are extremely small.
The Biden administration condemned the Iranian move, as did the governments of France, Germany and the United Kingdom, which said in a statement that “there has been a viable deal on the table since March, 2022” that Iran has rejected.
The escalation of tensions was worrisome, several experts said, and marked a hardening of the position of Iran’s government. It appeared to be reacting to a warning on Wednesday by the U.N. nuclear watchdog, the International Atomic Energy Agency, that Iran was only weeks away from producing enough enriched uranium to make a nuclear weapon. While some analysts believe Iran has already reached that milestone, it would take a year or two, most experts agree, for Iran to fashion that fuel into a weapon that could fit into a missile warhead.
The action on Thursday marked a significant, and perhaps final, unraveling of the agreement that the Obama administration reached with Iran seven years ago. That deal required Iran to ship out of the country 97 percent of its nuclear fuel and to dismantle most of its nuclear centrifuges, the machines that spin at supersonic speeds to enrich uranium for nuclear power plants — and, at higher levels of purity, for nuclear weapons.
Even after Mr. Trump abandoned the deal unilaterally, Iran remained in compliance for more than a year. But it refused to allow inspectors to visit some areas where there were suspicions of past nuclear activity. Slowly Iran has suspended the inspectors’ access to some monitoring equipment, and today it deactivated and removed surveillance cameras.
It is not the “final death knell” on reaching a deal, said Trita Parsi, an analyst and former president of the National Iranian American Council.
“But we’re extremely close,” he said. “The negotiations have been in a state of coma for the last few months, with no real progress and any movement.”
On Wednesday, Iranian state media announced that the government had shut off two cameras monitoring “an online enrichment monitor” at an unidentified site, hours before the United States, Britain, Germany and France submitted a resolution criticizing Iran to the International Atomic Energy Agency. Iran, the nations said, had failed to explain nuclear material detected at three undeclared sites. Although opposed by Russia and China, the resolution passed on Wednesday.
On Thursday, Iran told the I.A.E.A. it would begin removing 27 surveillance cameras and other monitoring equipment at several sites.
“We are in a very tense situation,” Rafael Mariano Grossi, the director general of the I.A.E.A, told reporters in Vienna on Thursday. He said that the sites included those in Tehran and the cities of Natanz and Isfahan, and that if an agreement were not reached within the next month, the latest update could be “a fatal blow” to the negotiations.
Although some 40 surveillance cameras remain active in Iran under other safeguard agreements, he said, the agency will lose important details within weeks about Iran’s nuclear activities on the ground.
The dismantlement of cameras and sensors at the Natanz site, a major enrichment center, would make it impossible for the I.A.E.A. to know how much uranium Iran is enriching, and how fast. It would also mean losing chain-of-custody information about the produced material, which is the assurance it doesn’t get diverted to a bomb project.
Iran had already been withholding access to data from some surveillance cameras at nuclear sites. It was unclear what would now happen to the data from the sites being cut off, Mr. Grossi said. Inspectors from the U.N. watchdog would be accompanying Iran’s teams as they removed monitoring equipment.
Losing the day-to-day data “is a blow,” said David Albright, a longtime expert on Iran’s nuclear program. He added that Iran was already close to achieving breakout capability — the ability to make a quick leap toward manufacturing a nuclear weapon before being detected. “They’re trying to rock the boat but not capsize it.”
The monitoring cameras were critical from a Western perspective because they were able to give inspectors an understanding of Iran’s fuel production rates, even if no inspectors were present.
“These are the eyes and ears,” Mr. Parsi said, adding that the instruments were able to send information to the I.A.E.A in real time. “We’ve lost a tremendous amount of insight into what is happening.”
The resolution that criticized Iran fell short on Thursday of a referral to the United Nations Security Council.
Iran has long maintained that its nuclear program is for peaceful purposes only. An assessment by American intelligence agencies in 2007 concluded that the country once had a nuclear weapons program but halted it in 2003.
Israeli officials have long opposed the 2015 nuclear deal, saying Iran was working toward building weapons, and Israel has repeatedly carried out attacks on the program, according to intelligence officials.
As negotiations were stalling last year, and after an Israeli attack on the plant at Natanz, Tehran said that it had begun enriching uranium to 60 percent at the site. Iran is also enriching uranium at Fordow, a facility embedded inside a mountain.
David E. Sanger contributed reporting.
