"International Atomic Energy Agency (IAEA) chief Yukiya Amano said he was still unable to provide 'credible assurance' Iran had no undeclared nuclear material and activities.
The talks -- which have dragged on for more than a year -- are aimed at setting limits on Iran's nuclear programme in return for an end to sanctions that have seriously hurt its economy.
As one of the conditions, Western officials say Iran must stop stonewalling the IAEA investigation into concerns Iran may have worked on designing a nuclear-armed missile...
'Iran has not provided any explanations that enable the agency to clarify the outstanding practical measures,' Amano told the U.N. agency's 35-nation board of governors, also meeting in the Austrian capital.
He was referring to information Iran was supposed to have given the IAEA by late August concerning allegations of explosives tests and other activity that could indicate preparations for developing nuclear bombs.
Those allegations were set out in an IAEA report in 2011 based on intelligence from some 10 IAEA member states as well as the agency's own investigation."