The International Atomic Energy Agency (IAEA) is pressing Tehran again for access to the Parchin military site as part of its probe into suspected nuclear weapons research in Iran.
Speaking outside Iran's diplomatic mission in Vienna shortly before the talks resumed, Iranian envoy Ali Asghar Soltan told reporters that both sides were trying to bridge disagreements, adding: "I hope for success".
The two sides are trying to unblock an IAEA investigation into Western suspicions, denied by Tehran, that Iran has been conducting research into nuclear weapons.
The meeting, the first since previous discussions ended in failure in June, takes place after an upsurge in rhetoric from Israeli politicians this month suggesting Israel might attack Iran ahead of the U.S. presidential election in November.
Iran denies allegations it is seeking a nuclear weapons capability. But its refusal to curb its nuclear enrichment program has prompted tough Western sanctions and heightened speculation that Israel may attack its atomic sites.
Iran 'Action Team' formed
The IAEA also recently disclosed that it is forming a special Iran team, drawing together experts in weapons technology, intelligence analysis, and radiation to oversee a probe of suspicions that Tehran has worked secretly on atomic arms.
Creating a unit focused on only one country is an unusual move for the International Atomic Energy Agency, reflecting the priority the U.N. nuclear watchdog is attaching to Iran.
One of diplomats likened the restructuring plan to the agency's Iraq 'Action Team' — the squad of experts who uncovered components of Saddam Hussein's fledgling nuclear-weapons program in the 1990s.
Danny Danon, deputy speaker of the Israeli Knesset and a member of Prime Minister Benjamin Netanyahu's Likud party, said on Thursday that Israel was "preparing for all scenarios". He was also dismissive of the agency's new Iran team.
"We are getting close to the point where the window of opportunity will be closed to us, and that's why you hear all those voices," he said when asked about the war rhetoric. "We have seen too many teams, too many summits, too much talk. It is about time to take action."
Separately, Reuters reports that Iran is hosting a summit of 120 developing nations beginning on Sunday as part of its three-year tenure as head of the Non-Aligned Movement (NAM).
The NAM was set up in 1961 to counter big power domination of international relations. About 35 heads of state or government are attending, including new Egyptian President Mohammad Mursi and United Nations Secretary General Ban Ki-moon.