The International Atomic Energy Agency (IAEA) has found uranium particles at a site in Iran that had not been declared by the Iranian authorities.
A confidential report, seen by the BBC, did not say exactly where the site was.
But inspectors are believed to have taken samples from a location in Tehran’s Turquzabad District.
That is the area where Israeli Prime Minister Benjamin Netanyahu has alleged Iran had a “secret atomic warehouse.
Iran has not responded to the report, but it has previously said the site was a carpet cleaning factory and served no clandestine purpose.
The IAEA’S report also confirmed Iran had resumed uranium enrichment at its underground fordo facility, breaching another commitment under its landmark 2015 nuclear deal with world powers. Enriched uranium can be used to make reactor fuel but also nuclear weapons..