Iran has breached the limit on the amount of enriched uranium it is allowed to hold, in violation of the nuclear deal it signed with the U.S. and other world powers in 2015, the state-run news agency IRNA reported Monday.

IRNA quoted Foreign Minister Mohammad Javad Zarif as making the announcement, and inspectors from the International Atomic Energy Agency, the U.N. nuclear watchdog, later confirmed that Iran had accumulated more enriched uranium than allowed under the deal.

A spokesperson for the agency said its director general, Yukiya Amano, had informed the Board of Governors on Monday that it had verified that Iran's total enriched uranium stockpile had exceeded 300 kg (661 pounds) of uranium enriched up to 3.67 percent U-235 "or the equivalent in different chemical forms" — the limit set by the nuclear deal.

Iran warned on June 17 that it would soon breach the terms of the agreement if the European signatories did not act to prevent tough sanctions being imposed by U.S. that stop foreign businesses from trading with Iran and buying its oil.

Enriched uranium is used in energy production, although stockpiling uranium is also a necessary step to building nuclear weapons, which Iran has denied doing. Iran has threatened to increase its enrichment of uranium closer to weapons-grade levels by July 7.

President Donald Trump is a longtime critic of what he called the "worst deal ever negotiated," and last year pulled the U.S. out of the agreement, which was secured under his predecessor, Barack Obama, and was signed by the U.K., France, Germany, Russia and China.

There can now be multilateral sanctions against Iran for breaching the terms of the agreement — although the deal was unlikely to be effective without American support.

The news comes amid rising tension between the U.S. and Iran. Trump called off an airstrike with minutes to spare after an American drone was shot down by Iranian forces on June 20.

Ali Arouzi reported from Tehran; Patrick Smith and Alex Holmes reported from London.