"I can confirm that officials are there in Natanz today," said a spokesman for the International Atomic Energy Agency.

"What they find and assess will be reported to the board," the spokesman added.

Iran said earlier it has started the process of producing 20 percent enriched uranium at a plant in the central city of Natanz, defying world powers who have warned of new sanctions unless Tehran halts its nuclear drive.

"From today we have started the 20 percent enrichment in a separate cascade in Natanz," Iran's atomic chief Ali Akbar Salehi told the official IRNA news agency.

The IAEA said its inspectors were frequently in Natanz as part of the agency's long-running monitoring and surveillance of enrichment activities there and pointed out that no new team had been sent out.

The watchdog has been investigating Tehran's controversial atomic drive for more than six years and teams of inspectors are routinely in Iran -- "more or less every other week" -- to monitor all of the Islamic republic's declared nuclear activities.

Some of the inspectors' initial findings on the higher enrichment activities could possibly be published in the IAEA's upcoming report on Iran, expected to be circulated among the agency's board of governors next week, according to diplomats in Vienna.

But since the switch to a higher level of enrichment had only started on Tuesday and the report was due out next week, it was unclear how detailed the information would be at this stage, the diplomats said.

In Tehran, Salehi said the separate cascade was "more on a lab scale", adding it had 164 centrifuges -- the devices which rotate at supersonic speed to enrich uranium.

"This can make between three to five kilograms (6.5 to 11 pounds) of 20 percent enriched uranium per month for the Tehran reactor," he said, referring to Iran's internationally-supervised facility which produces medical isotopes.

Salehi said the production is "twice" the needs of the reactor.

Iran has been conducting low level enrichment of uranium in the central city of Natanz for several years, in defiance of three sets of UN sanctions.

Iran's launch of the stepped-up enrichment process comes as the United States and France warned they will push for "strong" new UN sanctions against Tehran over its nuclear drive.

Western powers suspect Tehran is enriching uranium to make atomic weapons as the material in high purity form can be used in the fissile core of a nuclear bomb.

Iran insists its intentions are entirely peaceful and that it specifically wants to process uranium to the 20 percent level to fuel its Tehran research reactor.

The West is trying to convince Iran to sign on to an IAEA-brokered deal that envisages Tehran being supplied with nuclear fuel for the reactor in exchange for its low-enriched uranium (LEU).

The deal has hit a roadblock as Tehran, although saying it is ready "in principle" to sign on to it, insists that not all its LEU be shipped out in one go as world powers are demanding.

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