TEHRAN, Iran — President Mahmoud Ahmadinejad said Saturday that Iran now possesses 6,000 centrifuges, a significant increase in the number of uranium-enriching machines in its nuclear program, the semi-official Fars news agency reported.

The new figure is double the 3,000 centrifuges Iran had previously said it was operating in its uranium enrichment plant in Natanz.

"Islamic Iran today possesses 6,000 centrifuges," Ahmadinejad told university professors in the northeastern city of Mashhad.

The assertion that Iran has reached that goal is certain to further rankle the United States and other world powers. Washington and its allies have been demanding a halt to Iran's enrichment out of fear it is intent on using the technology to develop weapons.

Iran vehemently denies those allegations and says it is interested in enrichment only for its nuclear power program.

The White House said that Iran's pronouncement does not facilitate a resolution to the nuclear standoff.

"Announcements like this, whatever the true number is, are not productive and will only serve to further isolate Iran from the international community," said White House spokesman Carlton Carroll. "We have offered a generous incentives package to the Iranians, we urge them to suspend enrichment and accept the package. If they don't, more sanctions are the next step."

Ahmadinejad made the announcement a week after the U.S. reversed course by sending a top American diplomat to participate in negotiations with Iran, prompting hopes for a compromise.

But those talks fizzled when Iran refused to consider a revised deal that involves suspending enrichment, and the six negotiating powers — the U.S., Britain, France, Russia, China and Germany — gave Iran two weeks to respond positively or face a new round of sanctions.

Iran already is under three sets of U.N. sanctions for its refusal to suspend enrichment.

In April, Ahmadinejad said Iran had begun installing 6,000 centrifuges at Natanz. His reported comments Saturday provided the first public assertion that Iran has reached that goal.

Ahmadinejad asserted that Iran's interlocutors had agreed to allow it to continue to run its program as long as it was not expanded beyond 6,000 centrifuges, state radio reported.

"Today, they have consented that the existing 5,000 or 6,000 centrifuges not be increased and that operation of this number of centrifuges is not a problem," state radio quoted Ahmadinejad as saying on Saturday.

A report by the U.N.'s nuclear monitoring agency that was delivered to the 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."

Uranium can be used as nuclear reactor fuel or as the core for atomic warheads, depending on the degree of enrichment.

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 that can churn out enriched uranium at more than double the rate.

A total of 3,000 centrifuges is the commonly accepted figure for a nuclear enrichment program that is past the experimental stage and can be used as a platform for a full industrial-scale program that could churn out enough enriched material for dozens of nuclear weapons.

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

Ahmadinejad called the U.S. participation in the latest round of nuclear talks "a victory for Iran."

In a major shift in the Bush administration's policy, Undersecretary of State William Burns joined envoys from the five other nations in Switzerland at talks July 19 on Iran's nuclear program.

In the past, the U.S. said it would join talks only if Iran suspends uranium enrichment first.

"The presence of a U.S. representative ... was a victory for Iran, irrespective of the outcome. ... The U.S. condition was for Iran to suspend enrichment but they attended (the talks) without such a condition being met," Ahmadinejad was quoted as saying in the state radio report.

On Wednesday, Ahmadinejad praised the U.S. participation at the talks as a step toward recognizing Tehran's right to acquire nuclear technology.

The negotiating powers — the five permanent members of the U.N. Security Council plus Germany — have offered a package of technological, economic and political incentives in return for Iran's cooperation to suspend uranium enrichment or at least not to expand it.

The revised deal delivered last month — which Iran refused to consider at the talks July 19 — envisions a six-week commitment for Iran to stop expanding enrichment. In return, the six nations would agree to a moratorium on new sanctions for up to six weeks.

That is meant to create the framework for formal negotiations that the six nations hope would secure Iran's commitment to an indefinite ban on enrichment.