Herman Nackaerts, head of nuclear inspections at the IAEA, made the comment at a closed-door briefing for member states of the Vienna-based UN agency, diplomats said.
One diplomat quoted Mr Nackaerts as saying there “may be some ongoing activities at Parchin, which add urgency to why we want to go” there.
Mr Nackaerts did not specify what kind of activities might be taking place or whether they might involve efforts by Iran to conceal something, the diplomats added.
The IAEA wants to visit Parchin as part of its investigation into allegations that Iran is trying to militarise its civil nuclear programme. But despite two rounds of high-level talks, 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 south-east of Tehran, after issuing a report that suggested Iran was pursuing military nuclear technology.
The report said the IAEA had information that Iran had built a large containment chamber at the Parchin complex to conduct high-explosives tests of the kind needed to trigger a nuclear warhead detonation. There were “strong indicators of possible weapon development”.