VIENNA - Iran has expanded the number of centrifuges enriching uranium to almost 5,000 and this has made it harder for U.N. inspectors to keep track of the disputed nuclear program, according to an IAEA report seen by Reuters.
Friday's restricted International Atomic Energy Agency (IAEA) report also said Iran had increased its rate of production of low-enriched uranium (LEU) material, boosting its stockpile by 500 kg to 1,339 kg in the past six months.
Iran's improved efficiency in turning out potential nuclear fuel was sure to fan Western fears of the Islamic Republic nearing the ability make nuclear bombs, if it chose to do so.
David Albright of the Institute for Science and International Security, a think tank that tracks proliferation issues globally, said Iran now had accumulated enough LEU to convert into high-enriched uranium sufficient for one atom bomb.
But this would require reconfiguring Iran's centrifuge network, miniaturizing HEU to fit on a warhead - technical steps that could take 1-2 years or more -- and would not escape notice of UN inspectors unless done at an undeclared location.
There are no indications of any such secret site.
Iran says it is developing a uranium enrichment industry solely as fuel for electricity generation.
But it has stonewalled an IAEA investigation into alleged past research into bomb-making and continues to impose restrictions on IAEA inspections.
The U.N. nuclear watchdog report said Iran had 4,920 centrifuges, cylinders that spin at supersonic speed, being fed with uranium hexafluoride gas (UF6) for enrichment around the clock as of May 31, an increase of about 1,000 since February.
Another 2,132 centrifuges were installed and undergoing vacuum tests without material inside while a further 169 were being installed -- bringing Iran's total number of deployed centrifuges at its cavernous underground Natanz enrichment hall to 7,231 - with 55,000 eventually planned.
The agency has informed Iran that given the increased number of cascades being installed and the increased rate of production of LEU, improvements to the containment and surveillance measures at (Natanz) are required in order for the agency to continue to fully meet its safeguards objectives, the report said, referring to basic inspections.
The agency has proposed a solution and initiated discussions with Iran to that end.
A senior U.N. official familiar with the report said the IAEA was looking into changing the angles of its surveillance cameras and having Iran change the walking routes of workers handling equipment to keep pace with the nuclear expansion.
Up to now, Iran has been enriching with only a fragile, inefficient 1970s vintage machine known as the P-1, adapted from a model obtained from former Pakistani-run nuclear smugglers.
It continues to test small numbers of a more sophisticated design, known variously as P-2s, A-2s or A-3s, at a separate pilot facility at Natanz. These models could refine uranium 2-3 times as fast as the P-1, analysts tracking Iran's nuclear program estimate.