UN atomic watchdog chief Yukiya Amano and top aides will travel to Tehran on Sunday for talks with Iran's chief nuclear negotiator, a few days before Iran and world powers meet in Baghdad to discuss the broader nuclear dispute.
News of the rare visit came as Western diplomats said the International Atomic Energy Agency (IAEA) and Iran were making headway towards a framework deal on how to tackle concerns about Irans atomic activity.
The IAEA wants Iran to address issues raised by an agency report last year that revealed intelligence pointing to past and possibly ongoing activity in Iran of use in developing the means and technologies needed to build nuclear bombs.
Iran says the intelligence is fabricated, but the UN agency says its inspectors need access to sites, documents and officials to reach credible conclusions in its inquiry.
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 would meet on Monday with chief nuclear negotiator Saeed Jalili.
The last visit by an IAEA chief to Tehran was by Amano's predecessor, Mohamed ElBaradei, in October 2009.
Herman Nackaerts, head of IAEA nuclear safeguards inspections worldwide, and Assistant Director General Rafael Grossi will accompany Amano, the statement said.
The IAEA and Iran held talks this week in Vienna and had been due to meet again on May 21 in the Austrian capital. The IAEA will now visit Tehran instead, raising the stakes for a substantial outcome.
Amano, who has taken a blunter approach towards Iran and its nuclear program than ElBaradei, has previously said any visit by him to Tehran would need to yield concrete results.
Western diplomats accredited to the UN agency say Iran seems keen to agree a so-called "structured approach" - an outline of how to address the IAEA's questions - ahead of Baghdad in the apparent hope of gaining leverage there.
They say they would welcome any sign that Iran is prepared to stop four years of stonewalling an IAEA investigation based on Western intelligence suggesting Iran has researched ways to acquire the ability to produce nuclear bombs.
But they caution that it remains to be seen whether an understanding with the UN agency is implemented in practice, saying Iran in the past has used procedural haggling as a way to buy more time as its nuclear program advances.
Asked whether he believed a deal between the IAEA and Iran was now near, one Western diplomat said: "I believe it when I see it."
The IAEA's priority is Parchin, where its report found that Iran had built a large containment vessel over a decade ago to conduct high-explosives tests that the UN agency said were "strong indicators of possible" nuclear weapon development.
Western diplomats say they suspect Iran is cleaning the site to remove incriminating evidence, a charge Tehran dismisses.
Prime Minister Benjamin Netanyahu said Friday he is skeptical that Iran will agree to halt its nuclear program, accusing Iran of playing a "chess game" with the international community.
Netanyahu said "nothing would be better than to just see this issue solved diplomatically."
"But I have to say I see no evidence whatsoever that Iran is serious about ending its nuclear program," he said.
Iran says its nuclear program is for peaceful purposes, like energy production. The West and Israel suspect Iran is pursuing nuclear weapons. Israel says a nuclear weapon in the hands of Iran would threaten Israels survival.
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