By Fredrik Dahl
VIENNA, Aug 24 (Reuters) - The U.N. nuclear watchdog pressed Iran on Friday to address suspicions about nuclear bomb research in the Islamic state, pursuing diplomatic efforts to resolve the dispute before any possible military action by Israel or the United States.
A flurry of bellicose rhetoric from some Israeli politicians this month has ignited speculation that Israel might hit Iran's nuclear sites before the U.S. presidential election in November.
Tensions went up another notch on the eve of Friday's talks between Iran and the International Atomic Energy Agency (IAEA) when diplomatic sources said Iran had installed many more uranium enrichment centrifuges at its Fordow underground site.
While the new machines are not yet operating, the move reaffirmed Iranian defiance of international demands on it to suspend enrichment and may strengthen the Israeli belief that toughened sanctions are failing to make Tehran change course.
"Only yesterday we received additional proof that Iran is continuing accelerated progress towards achieving nuclear weapons and is totally ignoring international demands," Israeli Prime Minister Benjamin Netanyahu said on Friday.
The diplomatic sources also said satellite imagery indicated Iran had used a brightly coloured - possibly pink - tent-like structure to cover a building at a military site which the IAEA wants to inspect, raising new concerns about suspected cleansing of evidence of illicit past nuclear activity there.
Iran, the Jewish state's arch-enemy and a major oil producer, denies it is seeking nuclear weapons and has threatened wide-ranging reprisals if attacked.
Iran's envoy to the IAEA, Ali Asghar Soltanieh, said he expected progress in Friday's meeting. "Both sides are trying to bridge the gap," he told reporters at Iran's mission in Vienna.
Herman Nackaerts, the IAEA's global chief of inspections, said the aim was to reach an agreement on how to resolve the U.N. watchdog's questions about possible military dimensions to Iran's nuclear programme.
Nackaerts, heading the IAEA delegation, said he would reiterate his request for access to the Parchin military facility, where he believes Iran has undertaken explosives tests relevant for developing a nuclear weapons capability.
It was the first meeting between the two sides since discussions in early June petered out in failure, dashing previous hopes that an accord might be near.
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 still closely linked.
Washington says there is still time for diplomatic pressure to work in making Iran curb its enrichment programme, which is the immediate priority of the six powers - the United States, Britain, Russia, China, France and Germany.
Refined uranium can fuel nuclear power plants or nuclear bombs, depending on the level of enrichment.
European Union foreign policy chief Catherine Ashton, who leads the six powers' nuclear talks with Iran, urged Tehran to strike a deal with the IAEA on the agency's inquiry.
"We call on Iran to use today's meeting to come to give its agreement ... so that questions of substance could be addressed swiftly," her spokesman said in Brussels.
IAEA CHIEF NOT OPTIMISTIC
Iran says it seeks only civilian nuclear energy.
But its refusal to limit and open up its atomic activity to unfettered IAEA inspections that could determine whether it is purely peaceful, or not, has led to harsher punitive sanctions and louder talk about possible military action.
Western diplomats expected no big breakthrough on Friday but said Iran could offer a concession to inspectors - who want access to sites, officials and documents - in hopes of blunting their upcoming quarterly report on Iran, which is due next week.
In so doing, Iran would also seek to deflect a planned Western move to have the 35-nation IAEA board of governors, meeting next month, to formally rebuke Tehran over its failure to cooperate with the agency's inquiry.
So any Iranian concession should be treated with scepticism, one diplomat accredited to the IAEA said.
The IAEA's immediate priority is to gain prompt access to Parchin, even though Western diplomats say it may now have been purged of any evidence of nuclear weapons research, possibly carried out a decade ago.
Citing satellite images, the diplomats say Iran has demolished some small buildings and moved earth at Parchin.
On Thursday, diplomatic sources said the building believed to be housing an explosives chamber - if it is still there - had been "wrapped" with scaffolding and tarpaulin, hiding any sanitisation or other activity there from satellite cameras.
Iran says Parchin, about 30 km (20 miles) southeast of the capital Tehran, is a conventional military facility and has dismissed allegations aired about it as "ridiculous". It says a broad framework agreement for how the IAEA should conduct its inquiry is needed before possibly allowing access to Parchin.