VIENNA - UN nuclear inspectors will press Iran this week for a long-sought green light to visit a key military site, although suspected clean-up work may make it difficult to find evidence of any illicit atomic bomb research there.

Thursday's talks in Tehran could provide clues as to whether the Islamic state may now be more willing to start addressing growing international concerns over its disputed atomic activity following US President Barack Obama's re-election last month.

The stakes are high: Israel - widely believed to be the Middle East's only nuclear-armed power - has threatened military action if diplomacy fails to prevent its arch-foe from acquiring doomsday weaponry. Iran says it would hit back hard if attacked.

But Western diplomats are not optimistic about the chances of a breakthrough in the new discussions in the Iranian capital, after a series of meetings between Iran and the International Atomic Energy Agency (IAEA) this year failed to make headway.

The Vienna-based UN nuclear watchdog wants Iran to allow its inspectors to visit sites, interview officials and study documents as part of an IAEA investigation - largely stymied by Iranian stonewalling for four years - into possible military dimensions to the country's nuclear program.

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