VIENNA (AP) -- Diplomats on Monday confirmed a report that Iran has begun uranium enrichment at an underground bunker and said the news is particularly worrying because the site is being used to make material that can be upgraded more quickly for use in a nuclear weapon than the nation's main enriched stockpile.
The diplomats said that centrifuges at the Fordo site near Iran's holy city of Qom are churning out uranium enriched to 20 percent. That level is higher than the 3.5 percent being made at Iran's main enrichment plant and can be turned into fissile warhead material faster and with less work.
The move was expected, with Tehran announcing months ago that it would use the Fordo facility for 20 percent production. Iran began to further enrich a small part of its uranium stockpile to nearly 20 percent as of February 2010 at a less-protected experimental site, saying it needs the higher grade material to produce fuel for a Tehran reactor that makes medical radioisotopes for cancer patients.
But with the time and effort reduced between making weapons-grade uranium from the 20-percent level, the start of the Fordo operation increases international fears that Iran is determined to move closer to the ability to make nuclear warheads - despite insistence by the Islamic Republic that it is enriching only to make reactor fuel. Its dismissal of findings by the International Atomic Energy Agency of secret experimental work on a nuclear weapons program also worries the international community.
Iran recently threatened to blockade the Strait of Hormuz, an important transit route for almost one-fifth of the oil traded globally. Tehran also has been angered by the West's efforts to sanction Iran over its nuclear program, including a possible ban on European imports of Iranian oil.
Fordo's location increases concerns.
The facility is a hardened tunnel and is protected by air defense missile batteries and the Revolutionary Guard. The site is located about 20 miles (32 kilometers) north of Qom, the religious nerve center of Iran's ruling system. The semiofficial Mehr news agency quoted Iran's nuclear chief, Fereidoun Abbasi, as saying Sunday that "the enemy doesn't have the ability to damage it."
Built next to a military complex, Fordo was long kept secret and was only acknowledged by Iran after it was identified by Western intelligence agencies in September 2009.
Two diplomats spoke to The Associated Press on condition of anonymity because their information was confidential and based on an inspection of Fordo last week by the International Atomic Energy Agency.
They said 348 machines were operating at Fordo in two cascades - the linked up configuration needed to enrich. Two other cascades were nearly assembled but not working, they said. The centrifuges appeared to be the standard old-generation machines in use at the main enrichment site at Natanz and not advanced, more efficient prototype versions.
About 8,000 centrifuges are operating at Natanz, where five years of enrichment have turned out enough material for several nuclear warheads.
The Fordo startup was first reported Sunday by the daily Kaynan, a hardline newspaper close to Iran's Supreme Leader Ayatollah Ali Khamenei, who has the final word on all important matters of state. Abbasi was more circumspect, saying Saturday that his country will "soon" begin enrichment at Fordo.
It was impossible to reconcile the two reports. But the diplomats speculated that they could be a further reflection of divisions within Iran's ruling circles about how upfront the nation should be with nuclear activities that are drawing increasingly severe international penalties beyond four sets of U.N. Security Council sanctions.
Iran - which claims it only seeks nuclear reactors for energy and research - has sharply increased its threats and military posturing against stronger pressures, including U.S. sanctions targeting Iran's Central Bank in attempts to complicate its ability to sell oil.
A senior commander of the Revolutionary Guard force was recently quoted as saying Tehran's leadership has decided to order the closure of the Strait of Hormuz, a strategic oil route, if the country's petroleum exports are blocked. Revolutionary Guard ground forces also staged war games in eastern Iran in an apparent display of resolve against U.S. forces just over the border in Afghanistan.
Iranian officials have issued similar threats, but this was the strongest statement yet by a top commander in the security establishment.
"The supreme authorities ... have insisted that if enemies block the export of our oil, we won't allow a drop of oil to pass through the Strait of Hormuz. This is the strategy of the Islamic Republic in countering such threats," Revolutionary Guard deputy commander Ali Ashraf Nouri was quoted as saying by another newspaper, the Khorasan daily.
Adding to Iran-U.S. tensions, Iran's state radio reported Monday that a Tehran court has convicted an American man of working for the CIA and sentenced him to death.
Iran charges that as a former U.S. Marine, Amir Mirzaei Hekmati received special training and served at U.S. military bases in Iraq and Afghanistan before heading to Iran for his alleged intelligence mission. The radio report did not say when the verdict was issued. Under Iranian law, Hekmati, a dual U.S.-Iranian national has 20 days to appeal. His father, a professor at a community college in Flint, Michigan, has said his son is not a CIA spy and was visiting his grandmothers in Iran when he was arrested.
In an interview broadcast Sunday, U.S. Defense Secretary Leon Panetta said Iran is laying the groundwork for making nuclear weapons someday, but is not yet building a bomb. Panetta reiterated U.S. concerns about a unilateral strike by Israel against Iran's nuclear facilities, saying the action could trigger Iranian retaliation against U.S. forces in the region.
"We have common cause here" with Israel, he said. "And the better approach is for us to work together."
Panetta's remarks on CBS' "Face the Nation" reflect the U.S. administration's long-held view that Iran is not yet committed to building a nuclear arsenal, only to create the industrial and scientific capacity to allow one if its leaders to decide to take that final step.
President Barack Obama approved new sanctions against Iran a week ago, targeting the central bank and its ability to sell petroleum abroad. The U.S. has delayed implementing the sanctions for at least six months, worried about sending the price of oil higher at a time when the global economy is struggling.
The U.S. and Israel have said that all options remain open, including military action, should Iran continue with its enrichment program.