TEHRAN - The United States said on Tuesday that it wanted a UN sanctions resolution on Iran "within weeks" as Iran further expanded its nuclear programme in defiance of growing international pressure. The Islamic Republic, which denies its programme has military aims, said on Sunday it would enrich uranium to 20-percent purity for a reactor making isotopes for cancer patients. On Tuesday it announced the work had begun. The big powers have already stepped up discussions on next moves. Russia sent its strongest signal yet that it could back a fourth set of U.N. sanctions over Iran's nuclear programme. Defense Secretary Robert Gates told Fox News: "I think it's going to take some period of time -- I would say weeks, not months -- to see if we can't get another UN Security Council resolution." Western powers fear Iran is enriching uranium with a view to producing nuclear weapons. Tehran says the work is for electricity and medical purposes only. State television quoted Iranian nuclear agency chief Ali Akbar Salehi as saying that enrichment started at the Natanz facility under the supervision of the International Atomic Energy Agency. It showed footage of him giving the order via computer and scientists and officials around him shouting 'Allahu Akbar' (God is greatest). The enrichment followed a failure to agree on a swap with big powers, including Russia, under which Iran would have sent most of its low-enriched uranium abroad in return for 20-percent-pure fuel rods for the reactor. Iran currently enriches uranium to 3.5 percent purity. Salehi said Iran had set up a chain of 164 centrifuges to refine the uranium to 20 per cent purity. He said the production capacity was 3 to 5 kg a month, above the Tehran reactor's needs of 1.5 kg, ISNA news agency reported. There was no independent confirmation of the start-up. Centrifuges that had enriched to 3.5 per cent would need to be recalibrated for 20 percent production -- preparatory work that would normally take a month or two. A diplomat close to the IAEA said inspectors had noticed no such preparations before Monday. Although a nuclear bomb requires about 90 percent purity, getting to 20 percent is a big step because low-level enrichment is the most time-consuming and difficult stage of the process. Iran currently has no nuclear power plants able to use the low-enriched uranium it has already produced, and also lacks the technology to convert the 20 per cent pure uranium into the fuel rods needed to run the medical reactor.
