Nov. 20 (Bloomberg) -- Iran has produced the minimum amount of low-enriched uranium needed to make a bomb if it was processed to weapons grade, a scenario that would first require the expulsion of UN inspectors, arms-control experts said.

``There is definitely cause for concern,'' Andreas Persbo, a senior researcher at the London-based Verification Research, Training and Information Center, said by telephone today. ``Their uranium conversion operations are going quite well.''

The uranium is stored at the Natanz plant and monitored by the International Atomic Energy Agency, an arm of the United Nations that oversees adherence to the nuclear Non-Proliferation Treaty. At the current level of enrichment, the uranium could fuel a power station. The treaty prohibits further enrichment to weapons grade. Since March 2007, the IAEA has made 20 unannounced visits to Natanz, where it has remote surveillance equipment.

The IAEA said yesterday that Iran's stockpile of low- enriched uranium rose 31 percent since September to 630 kilograms (1,389 pounds). Persbo calculates that 630 kilograms could yield 15 to 22 kilograms of weapons-grade uranium, enough for the production of a device under the supervision of an expert bomb- maker.

Iran has been under UN investigation since 2003, after the U.S. and major allies alleged the country was seeking to develop nuclear weapons, a charge it denies. Iran, which says it wants nuclear energy to meet its demand for electricity, is under three sets of UN sanctions after the IAEA board referred the dispute to the Security Council in March 2006.

`Fully Under Inspection'

``At the moment, the uranium is fully under inspection,'' Rebecca Johnson, director of the London-based Acronym Institute for Disarmament Diplomacy, said today in a telephone interview. ``To change that would require Iran to get rid of the inspectors and the only way to do that would be to leave the nuclear Non- Proliferation Treaty.''

Both analysts estimate that it would take Iran at least one year to make enough bomb-grade uranium, if it were to leave the treaty and reconfigure its enrichment facilities.

Their comments followed a New York Times report today in which experts were cited as saying that yesterday's IAEA report shows Iran has enough enriched uranium to make a bomb if the country breaches its treaty obligations and masters the design of a warhead.

U.S. experts concluded in the National Intelligence Estimate in December that the Persian Gulf country, holder of the world's No. 2 oil and natural gas reserves, probably can't produce a bomb until 2010.

Highly Complex

``What we're talking about would be a major, major reconfiguration,'' Persbo said. ``The complexity would be quite high.''

Iran signed the Non-Proliferation Treaty in 1970. The accord gives countries the right to enrich uranium while foreswearing atomic weapons development. Withdrawing from the treaty would also entail risks beyond what North Korea faced in 2003 when it left the accord.

``The international community would do all it could to prevent that and Iran could face demands to return the nuclear facilities and material it had acquired through its NPT membership,'' Johnson said.

To contact the reporter on this story: Jonathan Tirone in Vienna at jtirone@bloomberg.net.

Last Updated: November 20, 2008 09:42 EST