VIENNA, Nov 15 (Reuters) Iran has made important strides toward transparency about its nuclear activities but key questions remain unresolved and it has significantly expanded uranium enrichment, a UN report said today.
The findings may open Iran to harsher UN sanctions due to Western suspicions it is secretly striving to make atom bombs and its defiance of UN demands to suspend enrichment.
Iran says it only wants electricity from atomic energy.
The International Atomic Energy Agency said it remained unable to verify Iran was not militarising enrichment at secret sites still denying inspector visits to anything but the few facilities of its declared civilian atomic energy programme.
''Iran's cooperation has been reactive rather than proactive,'' IAEA chief Mohamed ElBaradei's report said. ''Iran's active cooperation and full transparency are indispensable for full and prompt implementation of the work plan.'' In a disclosure likely to alarm the West, the report said Iran's number of centrifuges enriching uranium had soared 10-fold in the past year to 3,000, a level that could start industrial output of nuclear fuel.
But Iran was running the centrifuges at very low capacity, a senior UN official familiar with the report said.
Even if Iran fed uranium into 3,000 centrifuges at maximum rate for long periods, technical skill analysts believe Iran will need some time to achieve, it would need about 18 months to produce enough fissile material for one bomb, the official said.
The United States said the report showed Iran still defying the international community and giving only ''partial answers'', leaving no choice but to seek broader, biting sanctions.
UN officials familiar with the IAEA's inquiry said Iran's new cooperation was groundbreaking after years of stonewalling.
The report said Iran had provided much documentation and allowed interviews with involved nuclear officials related to its secret development of centrifuges in the 1980s and 90s.
These can refine uranium for power plant fuel or bombs.
''GETTING ANSWERS'' ''The agency has been able to conclude that answers provided on the declared past P-1 and P-2 centrifuge programmes are consistent with its findings,'' the report said. But more verification was needed to ensure declarations were complete.
The IAEA remained barred from workshops making the high performance P-2 centrifuge to replace the current old P-1 model.
''This is (still) an important step forward. We had two years of no movement and now we're getting answers,'' said one senior UN official. Another said: ''Of course it's not enough, but it does create more confidence for the future.'' Iranian President Mahmoud Ahmadinejad said the IAEA report showed Iran had been telling the truth about its nuclear plans and was right to resist Western pressure to halt the programme.
World powers agreed on Sept 28 to draft new sanctions for a vote by the UN Security Council unless the IAEA report, and a pending European Union report on talks meant to nudge Iran into a suspension, both yielded a ''positive outcome''.
The report may contain enough positive elements to widen the gap between the four big Western powers and Russia and China over what to do next -- act quickly or grant more time for Iran to come clean with IAEA investigators.
The White House and its ambassador at the United Nations, Zalmay Khalilzad, said the United States would press ahead working with allies on a new round of UN sanctions.
UN officials conceded the process could take longer than the end of year target they set, but said it was never realistic to expect Iran to bare all in short order on a programme it has equated with national pride, security and modernisation.
Iran has linked cooperation to a halt to further U.N.
penalties. Russia and China, both with Security Council vetoes, want to preserve strong trade ties with Iran and say isolating the Islamic Republic could lead to wider Middle East conflict.
If Security Council avenues remain blocked, European Union states could consider financial sanctions to back up a broad US embargo against the Islamic Republic.
The latest in ElBaradei's quarterly reports on Iran will be debated by the agency's 35-nation governing board on Nov. 22-23.
Reuters RC VP0218