Iranian President Mahmoud Ahmadinejad says the more the West pressures his country, the more it will pursue its nuclear ambitions. (Laurent Gillieron, Keystone/Associated Press)

Iran's decision to conceal the development of its second uranium-enrichment facility raises questions about other possible secret sites, according to a report prepared Monday by the UN's nuclear watchdog.

The International Atomic Energy Agency's seven-page report, based on inspections of Iran's nuclear site near the city of Qom, was delivered Monday in preparation for a meeting next week of the UN organization's 35-country board.

Iran gave UN inspectors access to the site in October, a month after Tehran revealed its existence to the surprise of the international community, particularly since Iran was already under three sets of sanctions over its main nuclear facility in Natanz.

Western countries, led by the United States, expressed fear Iran was using the sites to pursue a nuclear weapons program, while Iran argued the facilities were built to help power civilian reactors.

The international agency said the facility in Qom, called Fordo, was on schedule to begin enriching uranium in 2011. The report said Fordo could house about 3,000 centrifuges, far fewer than the 8,600-centrifuge capacity of the Natanz facility.

But a senior international official told The Associated Press that Fordo's capacity was enough to produce a little more than a tonne of enriched uranium annually, too little to fuel a nuclear plant but enough for a nuclear warhead.

The agency's report, however, did not address the facility's possible functions.

Nuclear talks at impasse

Investigators did say that Iran's late notification of the plant's existence has heightened concerns that other facilities not under the purview of the UN agency may be present.

The delay was "inconsistent with [Iran's] obligations" to the nuclear agency, the report said.

Iranian president Mahmoud Ahmadinejad warned the West not to pressure Tehran over its nuclear program, saying such a stance only makes the country more determined to pursue nuclear technology.

"Co-operation with Iran in the nuclear field is in the interests of Westerners," Ahmadinejad said in a statement posted late Sunday on the presidential website. "Their opposition will make Iran more powerful and advanced."

Iran is in talks to purchase nuclear fuel for use in its reactors but has backed off a UN-proposed deal that would see it ship its available supply of enriched uranium to Russia for further enrichment and has instead proposed buying the nuclear fuel it needs by other means.

That solution is unpalatable to the United States and its allies, who signed off on the UN-proposed draft plan because it would take uranium capable of being used for weapons out of Iran and replace it with fuel rods that could not be further enriched into weapons-grade material.

U.S. President Barack Obama recently said Iran is running out of time to agree to the UN-brokered plan.

The UN agency's "latest report on Iran underscores that Iran still refuses to comply fully with its international nuclear obligations," State Department spokesman Ian Kelly told Reuters.

"Now is the time for Iran to signal that it wants to be a responsible member of the international community. We will continue to press Iran … to meet its international nuclear obligations."

With files from The Associated Press