* Sanctions, outages have complicated Iran’s nuclear drive
* But uranium stockpile growing steadily anew
* Halt in November lasted only for a short while
* Experts: Iran may be able to build bomb within two years
By Fredrik Dahl
VIENNA, Feb 7 (Reuters) - Iran has resumed amassing enriched uranium at a steady pace after possible cyber sabotage and a mysterious albeit brief halt in its nuclear activities late last year, diplomats and experts say.
Technical woes, toughened international sanctions and the Stuxnet computer worm may all have figured in hampering Iran’s nuclear progress, potentially pushing back estimates for when it might be able to assemble an atomic bomb if it decided to do so.
But despite such problems, the Islamic Republic is pressing ahead with its disputed nuclear energy programme and its stockpile of low-enriched uranium (LEU) is continuously growing.
It is now believed to have enough material for one or two nuclear bombs if refined much further, even though it is unclear how soon it could build such a weapon, which would entail the technical feats of compressing highly-enriched uranium (HEU) into a missile cone and assembling a delivery vehicle.
Iran denies that its aim is to “weaponise” enrichment, saying it seeks only an additional source of electricity.
Assessments of delays or advances in Iran’s nuclear work have profound political significance as they can influence the amount of time major powers believe they have at their disposal to try to resolve the dispute diplomatically.
The risk of the row escalating into a military conflict appeared to recede last month when the departing head of Israeli espionage agency Mossad said Iran, the Jewish state’s arch-foe, might not have a nuclear weapon before 2015.
But that was later contradicted by the new head of Israel’s military intelligence, who said sanctions had not held up Iran’s nuclear programme and it could produce bombs within two years.
“On the whole, I do have a feeling that the enrichment programme is not in fantastic shape,” one senior Western diplomat said. But Iran keeps accumulating LEU and “there is no sense that ... that increasing trend is under threat”, he said.
Iran’s centrifuges producing enriched uranium, which can be used to fuel power plants or provide material for weapons if refined to a high degree, have been plagued by breakdowns since a rapid expansion of the process in 2007-08.
Western officials say stiffened sanctions on Iran, one of the world’s largest oil producers, are interfering with its enrichment programme by making it more difficult to obtain vital equipment and parts from abroad.
Covert operations by Israel or the United States, which have not ruled out military action to make sure Iran does not obtain an atomic bomb, may also have damaged its atomic activities.
Speculation that the Stuxnet computer worm was a state-directed cyber attack on Iran’s Natanz enrichment site was fuelled by revelations in November that it temporarily stopped refining uranium there in the middle of that month.
But the head of the U.N. atomic watchdog, which is due to issue its next, quarterly report about Iran’s nuclear programme by early March, told Reuters last week that the halt lasted only for a “short period of time”.
Yukiya Amano, director general of the International Atomic Energy Agency (IAEA), said he did not know the reason for the move but that LEU production was “continuing steadily”.
He did not give details. But diplomats believe Iran stopped feeding material into its centrifuges used to make LEU for at most a few days. Iran has not commented on the incident.
“This is a very difficult facility to operate,” Amano said.
The Institute for Science and International Security (ISIS), a Washington-based think-tank, said Iran’s nuclear programme was “suffering mounting setbacks”, giving more time for diplomacy.
That may well be needed. Two rounds of talks between Iran and six world powers -- the United States, France, Germany, China, Russia and Britain -- in December and January made no headway and ended without any agreement to meet again.
But despite disruptions, including centrifuge breakage and the assassination of two nuclear experts in 2010, ISIS said Iran had made some progress, increasing its monthly LEU output and boosting the number of working centrifuges late last year.
The senior Western diplomat said Iran’s nuclear programme presented a “patchy picture”, with both good and bad months for its LEU output. But whatever problems it might have, “when the guy has come to read the meter, it keeps on ticking over.”
Iran’s stockpile now exceeds three tonnes and it is estimated to grow by roughly 100 kg per month.
Proliferation analyst Mark Fitzpatrick said Iran experienced technical woes but that it already had a sizable amount of LEU.
“If further enriched, the current stockpile would be enough for one or two nuclear bombs,” Fitzpatrick, a former senior U.S. State Department official now at the London-based International Institute for Strategic Studies think-tank, said.
ISIS experts David Albright and Andrea Stricker said most analysts believed that Iran had not yet decided whether to build nuclear weapons, but that Tehran’s actions increasingly appeared to be working toward that capability.
“Predicting when Iran might obtain nuclear weapons is highly uncertain,” Albright and Stricker wrote in an analysis.
They cited U.N. experts as saying Tehran already has enough knowledge to assemble a crude weapon but that it faced problems in missile delivery. “If Iran built a secret site using more advanced centrifuges, it could be ready to build a bomb as soon as 2012 or 2013,” Albright and Stricker added.
Editing by Mark Heinrich