VIENNA, Austria — Iran’s new generation of advanced centrifuges have begun processing small quantities of the gas that can be used to make the fissile core of nuclear warheads, diplomats told the Associated Press yesterday.

The diplomats emphasized that the centrifuges were working with minute amounts of uranium gas. One diplomat said Tehran has set up only 10 of the machines — far too few to make enriched uranium in the quantities needed for an industrial-scale energy or weapons program.

Still, the information exposed details of the state of Iran’s experiments with its domestically developed IR-2 centrifuges, which can churn out enriched uranium at more than double the rate of the machines that now form the backbone of the Iranian nuclear project.

The existence of the IR-2 was made known only last week by diplomats accredited to the Vienna-based International Atomic Energy Agency, which is investigating Iran’s nuclear program for any evidence that it might have been designed to make weapons.

Diplomats told AP last week that the new centrifuges appeared to be running empty and they could not quantify the number of machines that had been set up at the experimental facility linked to Iran’s growing underground enrichment plant at Natanz.

Fleshing out previous information, a diplomat said yesterday that the IR-2 centrifuges were set up January 20 and began processing minute amounts of uranium gas soon afterward as part of testing the machines.

He and other diplomats who discussed the latest details of Iran’s program agreed to do so only if granted anonymity because they were not supposed to be releasing the confidential information.

Iran is under two sets of U.N. sanctions for ignoring Security Council demands that it suspend uranium enrichment, which Tehran started developing during nearly two decades of covert nuclear activity built on illicit purchases on the nuclear black market.

Iran insists the program is meant only to produce fuel for atomic reactors that will generate electricity, but the disclosure five years ago of the secret work heightened suspicions by America and others that the Iranians want to develop nuclear arms.

In rejecting U.N. demands that enrichment be halted until suspicions are cleared up, Iranian leaders have argued their country has a right to a peaceful nuclear program and insisted they would expand the project rather than freeze it.

Until last week’s reports that Iran had developed its own advanced centrifuge, Tehran had publicly focused on working with P1 centrifuges, outmoded machines acquired on the black market in the 1980s. More than 3,000 of the older centrifuges are processing uranium gas near Natanz, a city about 300 miles south of Tehran.

An IAEA report in November said Iran has stockpiled nearly 300 tons of the precursor gas used in enrichment. That would be enough to make about 40 nuclear bombs were it spun to weapons grade concentrations, experts have said.