Iran has acknowledged it had broken the limit set on its stockpile of low-enriched uranium by the 2015 nuclear deal.
It marks Tehran's first major departure from the unravelling agreement a year after the US unilaterally withdrew from the accord.
Iran had been expected for days to acknowledge it broke the limit after earlier warning it would do so.
It held off on publicly making an announcement as European leaders met to discuss ways to save the accord.
Iran has threatened to increase its enrichment of uranium closer to weapons-grade levels by July 7.
The announcement comes as tensions remain high between Iran and the US.
In recent weeks, the wider Persian Gulf has seen Iran shoot down a US military surveillance drone, mysterious attacks on oil tankers and Iranian-backed rebels in Yemen launching bomb-laden drones into Saudi Arabia.
The state-run Irna news agency quoted Iranian foreign minister Mohammad Javad Zarif as making the uranium announcement on Monday.
Irna reported that Mr Zarif, answering a reporter's question if Iran had broken the limit, said: "Yes."
The report did not elaborate.
The deal limited Iran to 300 kilograms of uranium enriched up to 3.67%.
The United Nations' atomic watchdog agency later confirmed Iran has surpassed the stockpile limit.
The International Atomic Energy Agency said its director general, Yukiya Amano, has informed its board of governors that the organisation had verified that Iran's stockpile of uranium enriched up to 3.67% had exceeded the 300kg allowed.