By Fredrik Dahl
VIENNA (Reuters) - Two senior U.N. nuclear watchdog officials who have been leading talks with Iran will leave this year, potentially robbing it of experience and expertise in dealing with Tehran over its disputed atomic program.
The management reshuffle coincides with apparent deadlock in the agency's push since early last year to coax Iran into allowing its inspectors to restart a long-stalled investigation into suspected atomic bomb research by the Islamic Republic.
Western diplomats blame Iranian stonewalling for the failure to come to an agreement, a charge Tehran denies, and some say the U.N. agency may soon need to reconsider its tactics. A new round of talks could be held in May.
"I think that we were approaching a potential re-set anyway. It is clear that Iran has been able to stall the process," a diplomat in Vienna said.
Rafael Grossi, assistant director general of the International Atomic Energy Agency, has been named Argentina's envoy to the Vienna-based IAEA, a job he is expected to start in the summer, a diplomatic source said on Friday.
The IAEA last month said a senior Finnish nuclear official, Tero Varjoranta, would succeed Herman Nackaerts when he retires in the autumn as chief nuclear inspector in charge of monitoring Iran's atomic activities and other sensitive issues.
Nackaerts, a Belgian, and Grossi have headed the IAEA's team of experts who have met nine times with Iranian envoys since early 2012 in an attempt - so far in vain - to secure access to sites, documents and officials in the country.
"Their departure deprives the agency of the two officials who have spent the most time in the last two years talking with Iranians at senior levels," said Mark Fitzpatrick of the International Institute for Strategic Studies think tank.
Analysts and diplomats stressed, however, that it is IAEA Director General Yukiya Amano, who steered the agency into a tougher approach to Iran, who decides policy. He secured a second four-year term in March, signaling continuity.
"An administrative reshuffle by the agency below Amano will likely have little impact on the Iran talks," said Mark Hibbs of the Carnegie Endowment think-tank.
The IAEA-Iran talks are separate from, but still closely linked to, broader diplomatic negotiations between Tehran and six world powers aimed at resolving the decade-old dispute peacefully and prevent a new Middle East war.
MILITARY BASE ACCESS
The last round of IAEA-Iran negotiations, in February, yielded no breakthrough. Another session in May is a "possibility," a diplomat in Vienna said on Friday.
Iranian state television, citing a source close to the Iranian negotiating team, denied a media report that the U.N. agency and Tehran had already agreed to meet in mid-May.
Amano this month said that some of the differences between the two sides were still "quite important". He said any deal with Tehran must enable effective IAEA verification work.
In late 2011, the IAEA published a report with a trove of intelligence indicating past research in Iran which could be relevant for nuclear weapons, some of which might still be continuing. Iran dismissed the findings as baseless or forged.
Iran denies Western allegations that it is seeking to develop the capability to build nuclear weapons, saying its atomic activities are aimed at generating electricity.
But its refusal to curb sensitive nuclear work that can have both civilian and military purposes and its lack of openness with IAEA inspectors have drawn tough Western sanctions.
(Additional reporting by Zahra Hosseinian in Zurich; editing by Mark Heinrich)