VIENNA (Reuters) - The U.N. nuclear chief will fly to Tehran on Sunday in an apparent bid to secure a deal enabling his inspectors to probe suspicions of atomic bomb research, a few days before Iran and world powers meet in Baghdad for broader talks on their dispute.
News of the rare visit came as Western diplomats said Iran and the U.N. watchdog were making headway towards a framework agreement on how to address concerns Tehran may be seeking to develop the capability to assemble nuclear weapons.
"I assume he wouldn't go without being fairly sure they will deliver," one Western diplomat said about the trip to the Iranian capital by Director General Yukiya Amano of the International Atomic Energy Agency, a Vienna-based U.N. body.
The IAEA wants Iran to clarify issues raised by an agency report last year that revealed intelligence pointing to past and possibly ongoing activity in the country of use in developing the means and technologies needed to build nuclear bombs.
Iran says the information is fabricated. The U.N. agency says its inspectors need access to sites, documents and officials to reach credible conclusions in its inquiry.
Amano is travelling to Tehran "in hopes of cementing" an agreement on the sensitive issue after four years of Iranian stonewalling of the agency's investigation, another envoy said.
The IAEA's priority is Parchin, where its report found Iran had built a large containment vessel over a decade ago to conduct high-explosives tests the U.N. agency said were "strong indicators of possible" nuclear weapon development.
Western diplomats accredited to the U.N. agency say they suspect Iran is cleaning the site to remove incriminating evidence. Tehran dismisses the charge but has resisted repeated requests for U.N. inspectors to go there.
But the diplomats also say Iran seems keen to agree a so-called "structured approach" - an outline of how to deal with the IAEA's questions - ahead of Baghdad in the apparent hope of gaining leverage there.
Iran, which denies Western accusations of a nuclear weapons agenda, says such an agreement is needed before it can consider allowing access to Parchin.
"Amano's visit is clear evidence that a deal between the IAEA and Iran is finally about to be consummated. Or at least Iran has given the IAEA clear reason to think so," said nuclear proliferation expert Mark Fitzpatrick.
Iran and the world powers involved in nuclear diplomacy - the United States, Russia, China, Britain, France and Germany - revived negotiations in Istanbul last month after a 15-month hiatus during which the West sharpened sanctions to an unprecedented degree - targeting Iran's oil trade and banks.
The resumption of diplomacy offers a chance to defuse that tension as well as worries about a new Middle East war. Their next meeting will take place in the Iraqi capital on May 23.
"Iran apparently wants to go into the Baghdad meeting with a positive wind at its back, demonstrating a posture of flexibility that it hopes will rebound to its benefit" in the meeting, said Fitzpatrick of the International Institute for Strategic Studies think-tank.
Israel, widely thought to have the Middle East's only nuclear arsenal and convinced a nuclear Iran would pose a mortal threat, has - like the United States - not ruled out air strikes to stop Iran's atomic progress if it deems diplomacy has failed.
The last visit by an IAEA chief to Tehran was by Amano's predecessor, Mohamed ElBaradei, in October 2009.
Amano "will travel to Tehran this Sunday ... to discuss issues of mutual interest with high Iranian officials," the IAEA said in a brief statement.
It said Amano, a veteran Japanese diplomat, would meet on Monday with Iranian nuclear negotiator Saeed Jalili, who is Iran's main representative in the talks with the world powers.
Herman Nackaerts, head of IAEA safeguards inspections worldwide, and assistant director general Rafael Grossi will accompany Amano. They were involved in talks in Tehran in January and February that failed to make notable progress.
The IAEA and Iran also held two days of discussions this week in Vienna and had been due to meet again on May 21 in the Austrian capital. The IAEA will now travel to Tehran instead, raising the stakes for a substantial outcome.
Amano, who has taken a blunter approach towards Iran and its nuclear programme than ElBaradei, has previously said any visit by him to Tehran would need to yield concrete results.
To foster progress in Baghdad, Iran should agree to grant IAEA access "without the conditions and limits" it proposed earlier this year, said Greg Thielmann of the U.S.-based Arms Control Association, an advocacy and research group.
Western diplomats say they would welcome any sign Iran is prepared to cooperate with the IAEA's investigation, which is largely based on Western intelligence suggesting Tehran has researched ways to acquire the ability to produce nuclear bombs.
But they caution it remains to be seen whether an understanding with the U.N. agency is implemented in practice, saying Iran in the past has used procedural haggling as a way to buy more time as its nuclear programme advances.
Asked whether he believed a deal between the IAEA and Iran was now close, one envoy said: "I believe it when I see it."
Editing by Sophie Hares