The report by the International Atomic Energy Agency (IAEA) also indicated that Iran was meeting its commitments under the Nov. 24 pact with the powers to curb its most proliferation-prone nuclear work in exchange for some easing of sanctions.
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It was issued to member states just hours after Iran and the six big powers - the United States, France, Germany, Britain, China and Russia - wound up a first round of negotiations in Vienna aimed at a final settlement of the decade-old dispute over Tehran's nuclear program. The next round is slated 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 aims.
Iran's reserve of uranium refined to a 20 percent fissile concentration fell to 161 kg in February from about 196 kg in November, the IAEA report said. Iran suspended higher-grade enrichment under the November deal and has since converted some of the material into oxide and diluted some to a lower purity.
However, the stock of low-enriched – or 5 percent purity – uranium rose to 7,609 kg from 7,154 kg in November. This apparently resulted from a delay in constructing a plant to convert some of the material into a form less suitable for processing into high-enriched bomb material.
Iran's holding of uranium – which Tehran says it needs to fuel a planned network of nuclear power plants – is closely watched in the West as it could provide weapons-suitable material if refined much further. Iran denies any such goal.