By Parisa Hafezi
TEHRAN (Reuters) - Iran said on Tuesday it would let U.N. nuclear investigators visit a military complex where they had been refused access to check intelligence suggesting Tehran has pursued explosives research relevant to nuclear weapons.
Western diplomats dismissed Iran's statement as a time-buying gambit - rather than a genuine shift towards nuclear transparency - with Israel talking increasingly stridently of last-resort military action against its arch-enemy.
Diplomats cited a proviso in the statement saying that access to Parchin still hinged on a broader agreement on how to settle outstanding issues which the two sides have long been unable to reach - an impasse that has put the West and Tehran on a slippery slope towards confrontation.
The West has sharpened sanctions against Iran to block its oil exports, a defiant Tehran has threatened to shut Gulf oil shipping lanes in reprisal while Israel has signaled it is losing patience with efforts to isolate the Islamic Republic.
Israel's Prime Minister Benjamin Netanyahu assured U.S. President Barack Obama on Monday that Israel has made no decision on attacking Iranian nuclear sites, sources close to talks in Washington said. He, however, gave no sign of backing away from possible military strikes.
Russia urged global powers on Tuesday to revive talks with Iran as soon as possible, saying an Iranian approach last month showed it was ready for serious negotiations. That perception is not shared by the United States, France and Britain. The last talks a year ago failed even to agree on an agenda.
An International Atomic Energy Agency report in November said that Iran had built a large containment chamber at Parchin, southeast of Tehran, to conduct high-explosives experiments that are "strong indicators" of an effort to design atomic bombs.
The IAEA requested access to Parchin during talks in Tehran in January and again in February, but the Iranian side refused.
"Considering the fact that Parchin is a military site, granting access is a time-consuming process and cannot be permitted repeatedly," Iran's delegation to the Vienna-based IAEA said in the statement.
It added that the "process could be ... started when the agreement on modalities is reached" - suggesting Tehran had not relaxed its insistence that there must first be an omnibus agreement on how to settle questions about the nature of Iran's nuclear work before an inspection trip to Parchin could happen.
Iranian diplomats and IAEA officials were not immediately available for comment.
Western suspicions about activities at Parchin date back to at least 2004, when a prominent nuclear expert assessed that satellite images showed it might be a site for research and experiments applicable to nuclear weapons.
IAEA inspectors did visit Parchin in 2005 but did not see the place where the U.N. watchdog now believes the explosives chamber was built.
Asked about Iran's statement, Western diplomats familiar with the matter told Reuters they saw an Iranian ploy to play for time, possibly to "sanitize" the Parchin site to eliminate any evidence of suspect activities before inspectors came.
One Western diplomat attending a meeting this week of the IAEA's 35-nation board of governors said the Iranian announcement was "nothing new, definitely not" a policy shift.
IAEA chief Yukiya Amano said on Monday the agency had "some indication that activities are ongoing at the Parchin site. It makes us believe that going there sooner is better than later."
He also said the IAEA continued to have "serious concern" about possible military dimensions to Iran's nuclear program. Iran says it is enriching uranium only for peaceful energy.
HISTORY OF FUTILE TALKS
There have been many prolonged, tortuous negotiations and procedural obstacles imposed by Iran since the IAEA first began seeking unfettered access in the country almost a decade ago to check indications of illicit military nuclear activity.
Diplomats say a broad deal on settling outstanding issues has been thwarted by Iran's refusal to let inspectors examine sites, peruse documents and question nuclear scientists cited in classified Western intelligence reports provided to the agency.
The IAEA named Parchin in a detailed report in November that lent independent weight to Western fears that Iran is working to develop an atomic bomb, an allegation Iranian officials deny, saying they are seeking only peaceful nuclear energy.
The report presented a trove of intelligence pointing to research activities in Iran of logical use in developing the means and technologies needed to assemble nuclear weapons, should it decide to do so.
At the IAEA governors meeting, the United States and its Western allies were seeking Russian and Chinese backing for a resolution against Iran to help isolate it over its failure to address the agency's growing concerns.
ISRAEL, U.S. DIFFER ON URGENCY OF THREAT
Israel has spoken of pre-emptive bombings against Iran, a hawkish approach that Obama - wary of the risk of igniting a new Middle East war and a global surge in oil prices as he seeks re-election in November - has tried to restrain Israel to give time for harsher sanctions and diplomatic pressure to bear fruit.
Obama and Netanyahu agreed on Monday to keep up coordination on Iran but continued to disagree on when the clock for non-military options to prevent Iran acquiring nuclear weapons capability should run out.
The Jewish state insists that military action against Iran would be warranted to prevent it from reaching nuclear weapons capability, as opposed to when it actually builds a device. Washington has not embraced that idea.
"The pressure (on Iran) is growing but time is growing short," Netanyahu was quoted by aides as telling Obama.
Later, addressing the influential pro-Israel lobby AIPAC, Netanyahu said: "None of us can afford to wait much longer. As prime minister of Israel, I will never let my people live in the shadow of annihilation."
At the podium, he held up a copy of a 1944 letter from the U.S. War Department to world Jewish leaders turning down their request to bomb the Nazi death camp of Auschwitz.
Obama sought to reassure Netanyahu that Washington was keeping its own military option open as a last resort and "has Israel's back." He added: "We do believe there is still a window that allows for a diplomatic resolution to this issue."
Israel, believed to be the only nuclear weapons power in the Middle East, fears Iranian nuclear facilities may soon be buried so deep that they would be invulnerable to its bunker-busting bombs, which are less powerful than those in the U.S. arsenal.
U.S. officials say that while Iran may be maneuvering to keep its options open, there is no clear intelligence that it has made a final decision to "break out" with a nuclear weapon.
(Reporting by Parisa Hafezi in Tehran and Fredrik Dahl in Vienna; Writing by Mark Heinrich in London; Editing by Diana Abdallah)