VIENNA (Reuters) - Iran has installed many more uranium enrichment machines in an underground bunker, diplomatic sources said on Thursday, potentially paving the way for a significant expansion of work the West fears is ultimately aimed at making nuclear bombs.
Iran denies allegations it is seeking a nuclear weapons capability. But its refusal to curb its nuclear enrichment program has prompted tough Western sanctions and has heightened speculation that Israel may attack its atomic sites.
In a possible sign of further Iranian defiance in the face of such pressure, several sources said Iran had put in place additional enrichment centrifuges in its Fordow facility, buried deep inside a mountain to protect it against enemy strikes.
One source suggested hundreds of machines had been installed.
In another development likely to worry the West, they said satellite imagery indicated Iran had covered a building at a military site which U.N. inspectors want to visit with a brightly-colored, tent-like structure.
Western diplomats have said they believe Iran is cleansing the Parchin site to remove any evidence of illicit nuclear activity at a place where the U.N. nuclear watchdog suspects it has conducted tests that had a military dimension.
Covering the building in question - which is believed to house a steel chamber for explosives experiments - may allow Iran to carry out sanitization or other work there which would not be seen via satellite pictures.
One Western envoy said that the suspected clean-up at Parchin was "intensifying" and that this made it doubtful that inspectors from the International Atomic Energy Agency (IAEA) would uncover any hard evidence there, even if they were allowed to go.
"Given the extent of the clean-up, it is indeed unlikely the agency, if it ever gets access, would find anything at Parchin," the diplomat said.
There was no immediate comment from Iran's mission to the Vienna-based U.N. atomic agency. It has previously dismissed the allegations about Parchin, which it says is a conventional military facility, as "ridiculous".
The IAEA will press Iran again in talks on Friday for access to Parchin as part of its long-stalled probe into suspected nuclear weapons research in the Islamic state, even though it concedes that the alleged sanitization would hamper its probe.
The meeting, the first since previous discussions ended in failure in June, takes place after an upsurge in rhetoric from Israeli politicians this month suggesting Israel might attack Iran ahead of the U.S. presidential election in November.
The talks are separate from Tehran's negotiations with world powers that have made little headway since they resumed in April after a 15-month hiatus, but the focus on suspicions about Iran's nuclear ambitions mean they are closely linked.
Lack of movement in both sets of talks could strengthen Israel's belief that tougher Western sanctions are failing to sway Tehran, its arch enemy, which has threatened wide-ranging reprisals if attacked.
Washington says there is still time for diplomatic pressure to work to force Iran to curb its nuclear enrichment program, which is the immediate priority for the six powers - which also include Britain, Russia, China, France and Germany.
Yet Iran is showing no sign of backing down over what it says is its inalienable right to civilian nuclear energy and has pushed ahead with expansion of Fordow since it was launched last year.
The site, near the holy Shi'ite Muslim city of Qom, is where Iran is enriching uranium to a fissile concentration of 20 percent, activity which the West wants it to stop immediately as it brings it closer to the level required for nuclear weapons.
"Our basic understanding is that they were continuing to install," a Vienna-based diplomat said, adding the new centrifuges at the site were not yet operating.
Another diplomatic source said Iran appeared to have completed installing two more cascades - interlocked networks of 174 centrifuges each - at Fordow.
If confirmed in a new IAEA report on Iran due next week, the two alleged new cascades would be in addition to six cascades that were previously installed, of which four were refining uranium. It was unclear when Iran may launch the new machines.
Editing by Andrew Osborn