Iran has breached the 300 kilograms of low-enriched uranium allowed under the 2015 international nuclear accord, both Foreign Minister Javad Zarif and the International Atomic Energy Agency (IAEA) confirmed on Monday.

The IAEA "verified on July 1 that Iran's total enriched uranium stockpile exceeded 300 kilograms," a spokesperson said.

The amount is well below that needed to produce one nuclear weapon. But the breach shows that Iran intends to ratchet up its response to the United States withdrawal from the Joint Comprehensive Plan of Action (JCPOA) last year and its reimposition of harsh unilateral sanctions.

On Twitter, Zarif insisted Iran was not violating the deal, citing the "Dispute Resolution Mechanism" of the treaty, which it believes the so-called E3+2 — Germany, France and the UK plus Russia and China — have not brought to a successful conclusion.

Fierce criticism from Israel, US warns Tehran

Israeli Prime Minister Benjamin Netanyahu, who has been highly critical of Iran's nuclear program, urged European countries involved in the Iran nuclear deal to impose "automatic sanctions."

"You committed to act the moment Iran violates the nuclear agreement, you committed to activate the mechanism for automatic sanctions that was set in the [UN] Security Council," he said in a statement.

Israel, he said, would "soon unveil more proof that Iran was lying all the time" about the program.

In a White House statement, the US government reiterated its opposition to the JCPOA, which it withdrew from in May of last year. "It was a mistake under the Iran nuclear deal to allow Iran to enrich uranium at any level," it said, adding that "the United States and its allies will never allow Iran to develop nuclear weapons."

US President Donald Trump was asked by reporters for his reaction to the latest news from Tehran and he said: "They know what they're doing. They know what they're playing with and I think they're playing with fire."

Read more: How Trump's sanctions are crippling Iran's economy

Iranian officials had warned that the country would likely exceed the uranium limit this week if the remaining signatories to the nuclear deal — China, Germany, France, Britain and Russia — failed to find a way for Tehran to receive the economic benefits promised in exchange for dismantling its nuclear program.

Iran is allowed to enrich up to 300 kg of uranium to 3.67% under the terms of the JCPOA. It has not gone over the 3.67% threshold, but has threatened to do so by July 7. About 1,500 kg of uranium enriched at around 90% is needed for one nuclear weapon.

Falling back under the 300 kg is easily reversible, and the remaining powers in the JCPOA would only become concerned if enrichment levels were ramped up to 20%, Francois Nicoullaud, a former French ambassador to Iran, told AFP.

"As long as Iran does not get close to a threshold of a ton of lightly enriched uranium, there is no pressing concern," Nicoullaud said. But if Iran "amassed, for example, a stock of 200 to 300 kilograms of uranium enriched to nearly 20% there would be cause for great concern."

The International Crisis Group, a conflict prevention non-profit, wrote in a January assessment that to strengthen its negotiating position Tehran "could creep past some of the JCPOA's boundaries both as a show of defiance and in hopes of pressuring the deal's remaining parties to do more to save it."

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The US exit from the deal and heightened tensions between Washington and Tehran in the Persian Gulf in recent months has had the European signatories to the JCPOA scrambling to save the accord.

After months of delay, European powers meeting with Iranian officials in Vienna last Friday announced the start of their so-called INSTEX scheme, a mechanism to facilitate EU-Iran trade in humanitarian goods not under US sanctions.

Trade between Europe and Iran has plummeted since the US imposed a raft of sanctions that have battered Iran's currency and sent its economy into recession. The Islamic Republic's oil exports to the bloc are down to zero.

After the talks on Friday, Abbas Araghchi, Iran's deputy foreign minister, said that Europe was not doing enough and for the INSTEX system to be useful "Europeans need to buy oil from Iran, or to consider credit lines for this mechanism."

ng, cw, jsi/aw (AFP, AP, dpa, Reuters)

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