A US nuclear monitor has published satellite images of an Iranian weapons facility which it says may be involved in work on nuclear arms.
Isis says Parchin complex shows suspicious structures (photo: DigitalGlobal/Isis)
Images of Parchin base show buildings that could be used to test nuclear bomb components, the Institute for Science and International Security said.
A US official said concern about the site should be included in a UN report on Iran's nuclear activities.
Iran says allegations it is hiding nuclear facilities at Parchin are lies.
A senior American delegate at the International Atomic Energy Agency, the UN's nuclear monitoring body based in Vienna, said satellite evidence "clearly shows the intention to develop weapons".
Nuclear experts have said the Parchin military complex, south-east of Tehran, may be a site for the research, testing and production of nuclear arms.
Iran insists its nuclear programme is solely for peaceful purposes.
The Isis images are said to show a structure for testing conventional explosives used in a nuclear device.
"This is a new lie, like the last 13 lies based on news reports that have been proved to be lies," Hossein Mousavian, Iran's chief delegate to the IAEA board meeting, said.
The IAEA board is currently deciding on a draft resolution to offer Iran a deadline to show it does not have a nuclear weapons programme.