The chief UN atomic inspector said Thursday that talks with Iran had failed again to reach a deal on agreeing enhanced inspections of Tehran's nuclear programme, and that no new meeting had been set.
"We had discussions on the structured approach document but could not finalise the document," Herman Nackaerts of the International Atomic Energy Agency told reporters at Vienna airport after returning from Tehran.
"Our committment to continued dialogue is unwavering. We will work hard now to resolve the remaining differences but time is needed to reflect on the way forward," he said.
"We haven't agreed yet on a date for the next meeting."
He declined to comment on whether the two sides had made any progress towards a deal.
Iran's envoy to the IAEA Ali Asghar Soltanieh was quoted Wednesday by the Iranian news agency ISNA as saying: "Some differences were resolved and agreement on some issues in the modality was reached."
"New proposals," Soltanieh said, had been put forward in the meeting but they would be discussed at "future meetings." He did not however give a date for a new round of talks.
The meeting was the latest in a string of failed talks at which the IAEA pressed Iran to grant access to sites, scientists and documents that the agency believes may have been part of a covert nuclear weapons drive.
Iran says that the IAEA's allegations are based on flawed Western intelligence -- which it has not been allowed to see -- and says it has never sought to develop the bomb.
This latest failure comes less than two weeks before talks between Iran and six world powers -- the United States, China, Russia, Britain, France and Germany -- in Kazakhstan on February 26.
These talks follow three rounds in 2012, the last in Moscow in June, at which the six, known as the P5+1, pressed Iran to scale back key areas of its nuclear programme.
Iran however walked away because the P5+1 stopped short of offering Tehran relief from UN Security Council and unilateral Western sanctions that last year began to cause major economic problems for the Persian Gulf country.