U.N. agency sees deal soon to check Iran nuclear work VIENNA (Reuters) - The United Nations nuclear agency expects to reach a deal with Iran next month enabling it to investigate whether the Islamic state has carried out atomic bomb research, the chief U.N. inspector said after returning from Tehran on Friday. Even though the International Atomic Energy Agency (IAEA) failed to gain requested access to the Parchin military complex during Thursday's visit to the Iranian capital, IAEA delegation head Herman Nackaerts said progress had been made. "We had good meetings," Nackaerts, deputy director general of the U.N. watchdog, told reporters at Vienna airport. World powers seeking to resolve a decade-old dispute over Iran's atomic activity and avert the threat of a new Middle East war closely watched the IAEA-Iran talks for any indication of Iranian readiness to finally start addressing their concerns. In Washington, the U.S. State Department sounded a cautious note, saying Iran had repeatedly raised obstacles to real progress. "While we do commend the IAEA for its efforts, we're disappointed that Iran did not grant access to the Parchin site which Iran has been sanitizing in advance of re-engaging with the IAEA," State Department spokesman Patrick Ventrell said. We understand there's going to be a meeting in January between the two sides and we hope that Iran starts the immediate, substantive cooperation that is long overdue. U.S. ally Israel - believed to have the Middle East's only nuclear arsenal - has threatened military action if diplomacy and economic sanctions intended to halt Iran's uranium enrichment work do not resolve the standoff. The IAEA and Iran, which denies Western allegations it is seeking to develop a capability to assemble nuclear weapons, will meet again on January 16, Nackaerts said. "We expect to finalize the structured approach and start implementing it then shortly after that," he said, referring to a framework agreement on how to tackle the IAEA's suspicions about possible military dimensions to Iran's nuclear program. Nackaerts did not give details on what had been achieved. But one stumbling block in previous, fruitless meetings was Iran's request for access to intelligence documents at the basis of the IAEA's concerns that Iran has conducted past, and possibly still ongoing, experiments relevant for atomic arms. Another bone of contention has been Iran's insistence that each specific area of the investigation should be declared closed once the IAEA's questions had been settled, while the U.N. agency wants to be able to return to the issue if needed. The IAEA had said after talks in May it expected a deal soon, but that failed to materialize. "We have now had so many false starts that there are grounds to be skeptical," said Shashank Joshi, a senior fellow and Middle East specialist at the Royal United Services Institute. Western diplomats, who often accused Iran of stonewalling and playing for time, want Iran to engage in substance on the IAEA's long-stalled inquiry and immediately give it access to sites, officials and documents it needs. "There will likely be many in Washington and Israel skeptical that this ... is anything but a delaying tactic on Iran's part," said Miles Pomper, senior research associate at the James Martin Center for Nonproliferation Studies. Iran says its nuclear program is a peaceful bid to generate electricity. But its refusal to curb activity which can have civilian and military purposes, and lack of openness with the IAEA, have drawn increasingly tough Western sanctions. The IAEA - which said before the trip it hoped to visit Parchin - was unable to go there this time but it would be part of the "structured approach" accord, Nackaerts said. The Vienna-based agency believes Iran has tested explosives with possible nuclear applications at Parchin, southeast of Tehran, and has repeatedly asked for access. Iran says Parchin is a conventional military site and has dismissed allegations that it has tried to clean it up before any visit. It says it must first agree a framework deal with the IAEA before allowing any visit. A senior Iranian diplomat said Tehran was open to an inspection of Parchin. But, Mostafa Dolatyar added in New Delhi, "if they want do it as a mouse-and-cat game of course it is not possible." Western diplomats say Iran has carried out extensive work at Parchin in the past year, including demolition of buildings and removal of soil, to cleanse it of any traces of illicit activity. The IAEA says going there would still be useful. The IAEA-Iran talks are separate from but closely linked to broader efforts by six world powers to resolve the nuclear row. Analysts and diplomats say there is a window of opportunity to make a renewed diplomatic push after last month's re-election of U.S. President Barack Obama. The six powers - the United States, Britain, France, Germany, Russia and China - want Iran to scale back its uranium enrichment program and cooperate fully with the IAEA. Iran wants the West to lift punitive measures hurting its economy. Additional reporting by Nidhi Verma and Frank Jack Daniel in New Delhi and Andrew Quinn in Washington; Editing by Michael Roddy and Mohammad Zargham