Iran is now operating 4,000 centrifuges at its uranium enrichment plant, a top official said Friday, moving the country's controversial nuclear program further out of the experimental stage onto an industrial level.

Deputy Foreign Minister Ali Reza Sheikh Attar told the official IRNA news agency following his Aug. 19 visit that Iran was also preparing to install further centrifuges at the enrichment plant in Natanz, central Iran.

"Right now, nearly 4,000 centrifuges are operating at Natanz enrichment plant," Attar said. "Currently, 3,000 other centrifuges are being installed."

Uranium is enriched into nuclear fuel by the centrifuges to power operate nuclear energy plants. The same process, however, can be used to produce the fuel for nuclear weapons.

For this reason, the United States and its allies have been demanding a halt to Iran's uranium enrichment — something Tehran has repeatedly refused to do.

A total of 3,000 centrifuges is the commonly accepted figure for a nuclear enrichment program that is past the experimental stage.

By reaching 4,000, the program is moving into an industrial-scale program that could churn out enough enriched material for dozens of nuclear weapons.

Experts, however, say Iran would need to change the way centrifuges are operating to actually produce weapons-grade uranium, something that would be difficult since the Natanz facility is under video surveillance by the U.N.'s nuclear watchdog agency, the IAEA.

Negotiations are underway with five permanent members of the U.N. Security Council plus Germany to halt Iran's uranium enrichment program or at least maintain it at the current level in exchange for a package of incentives.

Last month, however, Iranian President Mahmoud Ahmadinejad indicated that negotiations had come up with a deal whereby the enrichment program could continue as long as it was not expanded beyond 6,000 centrifuges.

A report by the U.N.'s nuclear monitoring agency that was delivered to the U.N. Security Council in May said Iran had 3,500 centrifuges, though a senior U.N. official said at the time that Iran's goal of 6,000 machines running by the summer was "pretty much plausible."

In the enrichment process, uranium gas is pumped into a series of centrifuges called "cascades." The gas is spun at supersonic speeds to remove impurities. Enriching at a low level produces nuclear fuel, but at a higher level it can produce the material for a warhead.

The workhorse of Iran's enrichment program is the P-1 centrifuge, which is run in cascades of 164 machines. But Iranian officials confirmed in February that they had started using the IR-2 centrifuge, which can churn out enriched uranium at more than double the rate.

Iran says it plans to move toward large-scale uranium enrichment that will ultimately involve 54,000 centrifuges.