The UN nuclear watchdog believes unspecified "activities" may be taking place at an Iranian military site which make its request to visit the Parchin facility more urgent, Western diplomats said on Wednesday.
Herman Nackaerts, head of nuclear inspections at the International Atomic Energy Agency (IAEA), made the comment about Parchin at a closed-door briefing for member states of the Vienna-based UN agency, diplomats said.
One diplomat who took part in Wednesday's briefing quoted Nackaerts as saying there "may be some ongoing activities at Parchin which add urgency to why we want to go" there.
Nackaerts did not specify what kind of activities may be taking place or whether they may involve efforts by Iran to conceal something, the diplomats added.
Another envoy cited Nackaerts as saying the agency monitored the site via satellite images.
The IAEA wants to visit Parchin as part of its probe into allegations that Iran is trying to militarise its civil nuclear programme. But despite two rounds of high-level talks in January and February Iran has not agreed to the agency's access request, insisting its nuclear work is entirely peaceful.
The IAEA asked to visit Parchin, a military complex southeast of Tehran, after issuing a report in November that suggested Iran was pursuing military nuclear technology. The report helped trigger the latest round of US and EU sanctions on Iran.
The report said the IAEA had information that Iran had built a large containment chamber at the Parchin complex to conduct high-explosives tests. There were "strong indicators of possible weapon development," the agency said.
Suspicions about activities at the Parchin complex date back to at least 2004, when a prominent nuclear expert said satellite images showed it might be a site for research and testing relevant to nuclear weapons.
UN inspectors did in fact visit Parchin in 2005. But they did not see the place where the IAEA now believes the explosives chamber was built