Iran's apparent reluctance to let UN inspectors visit a military site near Tehran underlines the uphill task they face in convincing the Islamic state to address suspicions it may be seeking to develop nuclear weapons, Western diplomats say.
They say the UN nuclear watchdog sought access to the Parchin complex during three days of talks in
the Iranian capital, so far without any sign that Iran would agree to it.
More talks are scheduled for later this month.
The International Atomic Energy Agency (IAEA) identified Parchin in a detailed report in November that lent independent weight to Western fears that Iran's disputed nuclear activities have military links, an allegation Iranian officials reject.
The UN agency has not said whether the issue was among those it raised during the January 29-31 discussions in the Iranian capital aimed at shedding light on possible nuclear-linked weapons work, but diplomats accredited to the IAEA said it was.
The senior IAEA team requested "access to Parchin, which Iran did not provide," one Western diplomat said.
He and others suggested that Iran had sidestepped the question rather than rejected it outright during the meetings with the IAEA delegation headed by the agency's global inspections chief, Deputy Director General Herman Nackaerts.
"They asked to see a particular site and they never got an answer," another envoy said.
Iranian officials were not immediately available for comment. Foreign Minister Ali Akbar Salehi this week described the Tehran talks as "very good," without giving details.
The IAEA said before its Tehran trip late last month that the overall objective was to "resolve all outstanding substantive issues," referring to its growing concerns of possible military dimensions to Iran's nuclear program.
But diplomats said the talks appeared to have made little concrete progress on the issues raised in the IAEA's report, which said Iran appeared to have worked on nuclear weapon design and secret research to that end may continue.
The outcome of the IAEA talks with Iran - a second round is planned for February 21-22 - is closely watched in Western capitals and Israel for signs of whether Iran's leadership may finally be prepared to give ground after a decade of pursuing its nuclear development goals or whether it remains as defiant as ever.
"There was nothing achieved on this visit and in fact the agency could not get Iran to engage on possible military dimensions questions at all," the Western envoy said.
"I was never optimistic. This just reinforces my pessimism."