(CNN) Iran's stockpiles of enriched low-grade uranium have exceeded the 300-kilogram limit set in a landmark 2015 nuclear deal, Foreign Minister Javad Zarif said on Monday according to the state-run IRNA news outlet.

The move is thought to be Tehran's first major breach of the accord since US President Donald Trump withdrew from the agreement last year. The deal limited Iran's uranium enrichment in exchange for an easing of international sanctions.

Global nuclear watchdog, the International Atomic Energy Agency, said that its inspectors on the ground in Iran had confirmed the development.

"We can confirm that IAEA Director General Yukiya Amano has informed the Board of Governors that the Agency verified on July 1st that Iran's total enriched uranium stockpile exceeded 300 kg of UF6 enriched up to 3.67% U-235 (or the equivalent in different chemical forms)," IAEA spokesman Fredrik Dahl said in a statement.

Zarif, one of the chief architects of the deal, said later in the day that Iran's stockpiling of more enriched uranium than permitted under the pact did not violate the Joint Comprehensive Plan of Action, or JCPOA, since it reserved the right to respond to Washington's withdrawal from the agreement and subsequent sanctions.

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