U.N. nuclear watchdog, Iran fail again to reach deal VIENNA (Reuters) - U.N. inspectors and Iran failed again in talks this week to revive an investigation into suspected nuclear arms research by Tehran, a setback for diplomatic efforts to resolve the atomic dispute with the Islamic Republic peacefully. Herman Nackaerts, deputy director general of the International Atomic Energy Agency (IAEA), said on Friday after returning from Tehran that his inspectors had not been granted the access they have long sought to a military site. A further round of negotiations was scheduled for February 12, he said, more than a year after the IAEA and Iran held their first in a series of so far largely fruitless meetings. In a separate note sent to the IAEA's member states about the negotiations over Wednesday and Thursday, seen by Reuters, it said "important differences" between the two sides remained and it had therefore not been possible to wrap up a deal. The absence of a breakthrough meant to help allay international suspicions over Iranian nuclear ambitions will disappoint world powers seeking a broader diplomatic settlement with Iran that would avert the threat of a new Middle East war. The Vienna-based IAEA made its best efforts to find a compromise and "one has to question whether there is any political will in Tehran to reach an agreement or whether they are just trying to buy time," one Western envoy said. I struggle to be optimistic about the February meeting. The IAEA's attempts to resume its long-blocked investigation in Iran are separate from but still related to negotiations between Tehran and six world powers, known as the P5+1, that may resume later this month after a seven-month hiatus. The IAEA, whose mandate is to forestall the spread of atomic weapons, has been trying for a year to negotiate a so-called structured approach with Iran giving its inspectors access to sites, officials and documents for their inquiry. The most immediate of the U.N. agency's concerns is to inspect the Parchin military complex southeast of Tehran where it believes explosives tests of use in developing nuclear weapons may have been carried out, something Iran denies. We could not finalize the structured approach to resolve the outstanding issues regarding possible military dimensions of Iran's nuclear programme. He gave no details. But one key sticking point has been Iran's insistence that each separate issue in the inquiry is declared closed once Tehran has addressed it, while the IAEA wants the flexibility to return to it if new evidence emerges. Nackaerts said as he left Vienna for Tehran on Tuesday that he hoped for immediate access to Parchin, where Western diplomats suspect Iran has been trying to cleanse the site of any traces of past, illicit nuclear-related activity. Iran, which denies accusations of a nuclear weapons agenda and says intelligence information pointing to that is forged, insists Parchin is a conventional military facility and has dismissed accusations of "sanitization" taking place there. Iran's stonewalling on Parchin was no surprise, former chief IAEA nuclear inspector Pierre Goldschmidt said. Tehran has "no reason" to open it up unless it is sure that no traces of nuclear-related tests would be found or it receives a firm guarantee from the world powers that any incriminating evidence would not be used against it, Goldschmidt told Reuters. Western diplomats were monitoring the IAEA-Iran talks for any indication as to whether Iran, under intensifying sanctions pressure over its nuclear defiance, may be prepared to finally stop what they see as its obstruction of the U.N. investigation. Israel, a U.S. ally believed to harbor the Middle East's sole nuclear arsenal, has threatened to bomb Iranian nuclear sites if it judges diplomacy and sanctions meant to curb Iran's uranium enrichment programme to have failed irretrievably. But the probability of an Israeli attack on Iran in 2013 is low, partly because Tehran is unlikely to make a dash to a bomb this year, said political risk consultancy Eurasia Group. In addition, "Israel can inflict only limited damage on Iran's nuclear facilities" if it attempted to attack by itself, Eurasia Middle East director Cliff Kupchan said in an analysis. Diplomats have said there is still an opportunity for world powers to renew a push for an overall negotiated solution to the dispute after U.S. President Barack Obama won re-election in November. Iran wants the West to first lift sanctions damaging its economy.