Uranium particles have been detected at an undeclared nuclear site in Iran, the United Nations nuclear watchdog said Monday.
In a confidential report obtained by news agencies, the International Atomic Energy Agency (IAEA) confirmed that manmade uranium particles had been discovered, without revealing the location of the undeclared site.
The report also confirmed that Iran is enriching uranium at its underground Fordow facility - a site where, under the 2015 nuclear deal with world powers, it had agreed not to carry out any enrichment or enrichment-related research.
The U.S. pulled out of the nuclear agreement last year.
Over the weekend, Iran began pouring concrete for a second nuclear reactor at its Bushehr power plant, which is monitored by the IAEA.
Tehran has said its nuclear activity is for peaceful purposes - namely, providing energy to the country.
Iran has said it intends to enrich uranium to 4.5%, slightly above the the 3.67% limit allowed under 2015 deal. But breaking that barrier was part of Iran's earlier steps away from the agreement as it calls for the other signatories to help it navigate around U.S. sanctions on its important oil exports. Enriching to 4.5% is far below the level needed to make a nuclear weapon.