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 Friday in Vienna 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 U.S. In recent weeks, the wider Persian Gulf has seen Iran shoot down a U.S. 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 Foreign Minister Mohammad Javad Zarif as making the uranium announcement. IRNA reported that Zarif, answering a reporter's question whether Iran had broken the limit, said: "Yes."
"If Europeans do what they have to do, our measures are reversible," Zarif said, according to IRNA.
Zarif did not say how much low-enriched uranium had on hand, IRNA said.
The United Nations' nuclear watchdog, the International Atomic Energy Agency, declined to say Monday whether Iran had broken through the limit.
"Our inspectors are on the ground and they will report to headquarters as soon as the (low-enriched uranium) stockpile has been verified," the agency said.
Breaking the stockpile limit by itself doesn't radically change the one year experts say Iran would need to have enough material for an atomic bomb, if to choose to pursue one. Iran long has insisted its nuclear program is for peaceful purposes, despite Western fears about it.
But by coupling an increasing stockpile with higher enrichment, it begins to close that one-year window and hamper any diplomatic efforts at saving the accord.
Under terms of the nuclear deal, Iran agreed to have less than 300 kilograms (661 pounds) of uranium enriched to a maximum of 3.67%. Previously, Iran enriched as high as 20%, which is a short technical step away from reaching weapons-grade levels. It also held up to 10,000 kilograms (22,046 pounds) of the higher-enriched uranium.
At the time of the 2015 deal, which was agreed to by Iran, the United States, China, Russia, Germany, France and Britain, experts believed Iran needed anywhere from several weeks to three months to have enough material for a bomb.
Zarif was quoted as also saying that the country remained on track to raise its enrichment if Europe did not take any additional steps toward saving the accord.
"The next step is about the 3.67% limitation, which we will implement too," he warned.