VIENNA, Oct 24 (Reuters) - The U.N. nuclear watchdog wants to inspect sensitive sites and meet important officials - including a mysterious military man - in Iran as part of an investigation into suspicions that Tehran may have worked on designing an atomic warhead.
The International Atomic Energy Agency and Iran meet on Monday for the 12th time since early 2012, with the IAEA hoping to resume its long-stalled inquiry into alleged nuclear bomb research by Iran, which denies such work.
Both sides signalled a desire to achieve progress after their last discussions about a month ago. This was the first meeting since President Hassan Rouhani took office in August, raising hopes of a thaw in relations with the West.
The IAEA talks are separate from - but closely linked to - broader negotiations between Tehran and six world powers on the decade-old nuclear dispute that could descend into a new Middle East war if it is not settled.
While the powers are pressing Iran to curb its enrichment of uranium, which can have both civilian and military uses, the IAEA is investigating allegations that it has also sought the know-how for turning such material into a nuclear missile.
WHAT DOES THE IAEA WANT?
The U.N. agency says it needs access to officials, sites and documents in Iran to help it clarify concerns about what it calls possible military dimensions to the nuclear programme. Two years ago, it published a report with a trove of intelligence indicating past work in Iran which could be relevant for developing atomic bombs, some of which might still be continuing.
The IAEA says it has obtained more information since that "further corroborates" the analysis in its 2011 report, which covered suspected activities ranging from explosives testing to research on what analysts describe as an atomic bomb trigger.
Other issues it wants Iran to address include alleged detonator development, computer modelling to calculate nuclear explosive yields, and preparatory experimentation that could be useful for any atomic test. It says the "overall credible" information comes from member states - believed to include Western powers and Israel - as well as its own sources.
Over the last decade, the U.N. agency has become "increasingly concerned" about possible activities related to the development of a nuclear payload for a missile, the IAEA said in its latest quarterly report on Iran, issued on Aug. 28.
U.N. nuclear inspectors regularly visit Iran's declared atomic facilities but the agency says they also need to have wider access to ensure that there are no hidden activities.
In meetings since January 2012, the U.N. agency has been trying to negotiate a framework deal with Tehran to define how the inquiry should be conducted.
Contentious points that have prevented agreement include whether the IAEA should be allowed to return to topics it has already investigated, and Iran's demand to be given intelligence documents which form the basis of the allegations.
WHY DOES THE INVESTIGATION MATTER?
Western diplomats and nuclear experts say the IAEA needs to complete its inquiry to establish what happened and to be able to provide assurances that any "weaponisation" work has ceased.
The IAEA's 2011 report painted a picture of a concerted weapons programme that was halted in 2003 - when Iran came under increased Western pressure - but it also indicated that some activities may later have resumed.
"If Iran seeks to continue to hide its past military nuclear efforts, it may find that no amount of limitations and transparency on its current programmes is enough to reassure the international community," said David Albright of the Institute for Science and International Security, a U.S. think-tank.
WHAT DOES IRAN SAY?
Denying any atomic arms ambitions, Iran says the allegations about nuclear weapons-related work are baseless and forged by its enemies in the West and Israel. It has also rejected Western accusations that it is stonewalling the IAEA's investigation.
Iranian officials have said they are ready to respond to the IAEA's concerns but that a framework accord must be struck that safeguards its national security interests and ensures the investigation does not run for ever.
WHY IS PARCHIN IMPORTANT?
The IAEA has repeatedly demanded access to a site at the sprawling Parchin military base southeast of Tehran, where it believes Iran carried out high explosives tests in a steel chamber, perhaps a decade ago. It says such tests would be strong indicators of possible atomic bomb development.
In view of suspected Iranian efforts to remove any traces of illicit activity at Parchin the agency says its inspectors may no longer find anything if allowed to go there but that it still wants to visit the facility. The IAEA says it also needs answers to its "detailed questions" about Parchin. Iran says it is a conventional army base, and rejects the clean-up charge.
WHO IS MOHSEN FAKHRIZADEH?
A shadowy military man believed to be at the heart of Iran's atomic activities, Mohsen Fakhrizadeh, is likely to be at the top of the IAEA's list of officials it would like to interview, although it has not publicly confirmed this.
The IAEA's 2011 report identified him as a major figure in suspected work to develop technology and skills needed for making atomic bombs, and suggested he may still play a role. Western nuclear experts say he probably lives under tight security and in secrecy to keep him beyond the reach of assassins and U.N. investigators. (reporting by Fredrik Dahl; editing by David Stamp)