(Deletes word in paragraph 20)
* UN nuclear chief hints at possible Iran site "cleaning"
* Western powers, Russia, China show unity before Iran talks
* Iran: suspicions of bomb tests, cover-up are "ridiculous"
* Israel seeks advanced U.S. bunker buster bombs to hit Iran
By Fredrik Dahl
VIENNA (Reuters) - The U.N. nuclear watchdog does not rule out that Iran may be trying to remove evidence from a military site that inspectors want to visit as part of an inquiry into suspected research relevant to atomic bombs, the agency's chief said on Friday.
Yukiya Amano's comments, in an interview with Reuters, came a day after six world powers demanded Iran keep its promise to let international inspectors visit the Parchin military complex.
Their joint call demonstrated firmer resolve among the powers on Iran before a planned revival of high-level talks, as well as widening disquiet about the nature of Tehran's nuclear ambitions, with Israel threatening last-ditch military action.
Iran refused access to Parchin, southeast of Tehran, during two rounds of talks with a senior team of the International Atomic Energy Agency (IAEA), the U.N. agency dedicated to stopping the spread of nuclear weapons, in Tehran this year.
Western diplomats say Iran may be delaying inspectors' access to the site to give it time to sanitize the facility of any incriminating evidence of explosives tests that would indicate efforts to design nuclear weapons.
"We have information that some activity is ongoing there," Amano, IAEA director general, said at agency headquarters.
Asked whether he was concerned that Iran may be trying to whitewash the site, he said: "That possibility is not excluded ... We cannot say for sure because we are not there."
The veteran Japanese diplomat added: "We have to go there."
Iran, which rejects Western accusations that its nuclear programme is a covert bid to develop atomic bombs, has dismissed suspicions aired about Parchin as "ridiculous" and "childish".
An IAEA report last year revealed a trove of intelligence pointing to research activities in Iran of use in developing the means and technologies needed to assemble nuclear weapons, should it decide to do so.
The U.N. agency's document lent independent weight to Western suspicions and paved the way for the United States and its European allies to dramatically ratchet up punitive sanctions against Iran, targeting its lifeblood oil exports.
One salient finding in the report was information that Iran had built a large containment chamber at Parchin in which to conduct high-explosives tests that the IAEA said are "strong indicators of possible weapon development".
Heaping pressure on Iran to come clean, the United States, Russia, China, Britain, France and Germany used a U.N. nuclear watchdog governors' meeting on Thursday to urge Tehran to promptly open Parchin to IAEA examination.
They voiced concern that no deal was reached between Iran and IAEA inspectors at talks in January and February, "including on the access to relevant sites in Iran, requested by the agency ... We urge Iran to fulfil its undertaking to grant access to Parchin."
GETTING RID OF TELLTALE EVIDENCE?
Amano's deputy, Herman Nackaerts, told Thursday's closed session of the IAEA board of governors session, according to one participant: "Due to major differences between Iran and the agency, agreement could not be reached."
Nackaerts, the IAEA's chief safeguards inspector, said it had information from satellite pictures showing "the precise location where we believe an explosive chamber is situated".
Iran media reports this week suggested a visit to Parchin might still be granted but the IAEA said on Thursday Tehran had not contacted it formally about any trip.
Western diplomats briefed by a senior IAEA official last week said satellite images suggested activity at Parchin which they said might indicate a possible effort to erase evidence.
Asked whether he wasn't concerned that, when and if Iran allows access to the site, whatever the agency wanted to look at would no longer be there, Amano told Reuters:
"That possibility exists. That is one of the reasons why we say (going there) sooner is better."
The six powers made no mention of "sanitising" the Parchin premises in their statement at this week's session of the 35-nation board of the IAEA, the Vienna-based U.N. agency.
But their language regarding Parchin and other aspects of Iran's shadowy nuclear programme sent a message to Tehran of a more cohesive approach to tackling the stand-off. Russia and China have often opposed Western efforts to isolate Iran.
The festering nuclear dispute is stirring increased fears of war that could inflame the Middle East and send oil prices skyrocketing at a time of global economic downturn.
The six powers voiced "regret" about Iran's escalating campaign to enrich uranium, which can yield material for electricity or nuclear bombs and is now centred in a mountain bunker chosen as protection from air strikes.
Iran denies suspicions of a camouflaged attempt to develop atom bombs, insisting it wants nuclear power for electricity generation and medical treatments only.
Israel, regarding Iran's nuclear advances as a mortal threat, doubts sanctions and diplomacy will rein in its arch-enemy and is speaking more stridently of resorting to pre-emptive bombings of Iranian nuclear sites.
ISRAEL SAYS TIME RUNNING OUT
Prime Minister Benjamin Netanyahu said Israel would give sanctions on Iran a chance to work and would not attack its nuclear installations in the coming days or weeks.
"I am not standing with a stopwatch in hand. It is not a matter days or weeks, but also not a matter of years. Everybody understands this," he told Israeli television Channel 10.
Israel, believed to harbour the Middle East's only nuclear arsenal, has asked the United States for advanced "bunker-buster" bombs and refuelling planes that could improve its ability to attack Iran's underground nuclear sites, an Israeli official said on Thursday.
A U.S. official confirmed Netanyahu and Defense Secretary Leon Panetta discussed military capabilities but said no deals were struck during those talks.
A U.S. Air Force general said a 30,000-pound (13,600-kg) bunker buster bomb designed to smash through some 200 feet (65 metres) of concrete before exploding is a "great weapon" that could be used by U.S. forces in a clash with Iran.
Temporarily quieting the sabre-rattling, the European Union's foreign policy chief announced on Tuesday the powers had accepted Iran's offer to revive talks after a year's standstill.
The Islamic Republic's chief nuclear negotiator Saeed Jalili last month promised to float "new initiatives" at the talks, whose venue and date are not yet decided.
But Iran's ambassador to France, Ali Ahani, said on Thursday its "inalienable" right to enrich uranium would not be on the table - a stance redolent of past talks that ran aground over an inability to agree even on an agenda.
Obama on Monday warned against "bluster" and "loose talk of war" over Iran, which he felt had driven up oil prices, and said he was convinced "that an opportunity remains for diplomacy - backed by pressure - to succeed".
Iran's Supreme Leader Ayatollah Ali Khamenei hailed Obama's reference to opportunity. "We heard two days ago that the U.S. president said that (they) are not thinking about war with Iran. These words are good words and an exit from delusion," Khamenei was quoted by the official IRNA news agency as saying.
But Khamenei's praise for a U.S. leader, rare for Iran's paramount conservative clerical leader, was tempered by criticism of what he called an Obama remark about "bringing the Iranian people to their knees through sanctions".
The United States has succeeded in severely limiting Iran's access to global