VIENNA (REUTERS) - The size of Iran's most contested uranium stockpile has declined significantly for the first time in four years following a landmark nuclear deal with world powers in November, the UN atomic watchdog reported on Thursday.
As a result, Iran's holding of uranium gas enriched to a fissile purity of 20 per cent - a relatively short technical step away from the level required for nuclear weapons - is now well below the amount needed for a bomb, if processed more.
That stockpile is closely watched: Israel, Iran's arch-enemy and believed to be the Middle East's only nuclear-armed power, warned in 2012 that there would be a "red line" for possible military action against Iranian nuclear sites if its Tehran amassed enough such refined uranium for a single bomb.
Iran agreed under a Nov. 24 deal with six big powers to shelve its 20 per cent enrichment, begun in 2010. It has since diluted some of this uranium to a lower concentration and converted some into less proliferation-prone oxide.
"That decrease has been quite important," a senior diplomat familiar with Iran's nuclear programme said, and the "progress has been quite substantial in terms of inventory." Thursday's report by the International Atomic Energy Agency (IAEA) also showed, as reported by Reuters earlier this week, that the Islamic Republic was meeting its commitments under the November accord to rein in its most sensitive nuclear activity in exchange for some relief from economic sanctions.
"Things are progressing as planned," the diplomat said.
The IAEA report was issued to member states just hours after Iran and the six powers - the United States, France, Germany, Britain, China and Russia - completed a first round of negotiations in Vienna aimed at a final settlement of the decade-old dispute over the nature of Tehran's nuclear activity.
The next round was set for March 17.
UN nuclear inspectors are playing a critical role in monitoring that Iran is living up to its side of last year's six-month accord, designed to buy time for the negotiations on a comprehensive agreement over atomic activity Tehran says is entirely peaceful but the West fears may have military designs.
Iran's reserve of 20 per cent uranium gas fell to 161 kg in February from about 196 kg in November, the IAEA said. About 250 kg is needed for the core of one nuclear warhead, experts say.
Iran justified its 20 per cent enrichment drive by saying it was meant to replenish the fuel supply of a Tehran medical research reactor, but Western officials were sceptical, saying Iran had refined far more than it required for such a purpose.
However, the IAEA report showed the stock of low-enriched uranium (LEU) - or 5 per cent purity - increased to 7,609 kg from 7,154 kg in November.
This arose apparently from a delay in building a plant to convert some of the material into an oxide form less suitable for processing into high-enriched bomb material.