Senior U.N. nuclear inspectors and Iran ended two days of talks in Tehran on Thursday with no sign of a breakthrough in unblocking their investigation into suspected atomic bomb research in the Islamic state, Reuters reported.
Iran's ISNA and Fars news agencies reported that a further meeting between the International Atomic Energy Agency (IAEA) and Iran would be held on February 12 in the Iranian capital, but gave no details.
The Vienna-based U.N. agency had hoped to finalize an elusive framework deal with Iran this week that would allow the IAEA to resume a long-stalled inquiry into suspected military dimensions to the country's nuclear program.
Diplomats in Vienna said they did not yet have a read-out on how the talks in the Iranian capital had ended, but made clear they were not optimistic that an agreement had been struck.
They said they believed there had still been key differences during Thursday's discussions.
The IAEA team led by Deputy Director General Herman Nackaerts was due to return to Vienna early on Friday, a diplomatic source said. There was no immediate comment from the U.N. agency.
The IAEA, whose mission is to prevent the spread of nuclear weapons, has been trying for a year to negotiate a so-called structured approach with Iran giving the inspectors access to sites, officials and documents for their long-stalled inquiry.
World powers were monitoring the IAEA-Iran talks for any signs as to whether Tehran, facing intensifying sanctions pressure, may be prepared to finally start tackling mounting international concerns about its nuclear activity.
The six powers - the United States, France, Germany, China, Russia and Britain - and Iran may resume their separate negotiations later in January to try to reach a broader diplomatic settlement. They last met in June.
Israel - a U.S. ally believed to have the Middle East's only nuclear arsenal - has threatened military action if diplomacy and economic sanctions intended to rein in Iran's uranium enrichment program do not resolve the stand-off.
Iran denies Western accusations that it is seeking to develop a nuclear weapons capability, saying its program is aimed only at power generation and medical research.