International nuclear inspectors reported on Friday that Iran had finally begun operating a new generation of equipment that over time should give it the capability to produce nuclear fuel much faster, after years of delays made worse by Western sanctions and sabotage.

The equipment, new centrifuges that the inspectors described in a report circulated to members of the International Atomic Energy Agency, is intended to replace balky, breakdown-prone machines whose design Iran first bought from Abdul Qadeer Khan, a Pakistani who illicitly sold production equipment and bomb designs. Five years ago, President Mahmoud Ahmadinejad of Iran declared that the machinery, which he claimed was made in Iran, would soon be deployed. It became clear that his boast was premature.

Iran has ignored four sets of United Nations Security Council resolutions to cease enriching uranium. But it took until this summer for the country to begin using 54 of the new centrifuges, which the Iranians call the IR-2 and claim were produced entirely in its own small factories.

Because the machines spin much faster than the models they are intended to replace, they could speed Iran’s ability to enrich large quantities of nuclear fuel. The Central Intelligence Agency, in its assessments of Iran’s capabilities, has expressed doubts that the machines shown to inspectors would be used for producing weapons-grade material, but they have warned that the installation at the uranium enrichment complex at Natanz might be intended to work out bugs and that Iran could have secret facilities.

“What worries us is not what the Iranians show the inspectors, but what it tells us about what they know how to produce,” one senior intelligence official said.

Just installing the small number of IR-2 centrifuges, and a handful of more advanced models called the IR-4, was something of a victory for Iran in its cat-and-mouse game with the West. The United States and its allies went to extraordinary lengths to prevent Iran from obtaining crucial supplies, including blocking the export of a special form of steel needed to operate the equipment at high speed. Hundreds more machines would be needed before Iran had the capability to ramp up production significantly.

The software worm known as Stuxnet, which hit Iran more than a year ago and slowed progress toward obtaining nuclear weapons training, was aimed at the first-generation centrifuges, which Iran called the IR-1 (for Iran-1). That equipment came from the Khan network of illicit suppliers. Yet the IR-1s were so notoriously unreliable that they broke down even when they were not the target of cyberattacks.

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