Iran said Monday that it has exceeded the stockpile limit for low-enriched uranium allowed under the 2015 nuclear deal between Iran and world powers because Europe has failed to mitigate the impact of U.S. sanctions, a move that could add to the friction between Tehran and Washington.

The International Atomic Energy Agency, the United Nations’ nuclear watchdog, confirmed that Iran’s stockpile of low-enriched uranium exceeded the 300-kilogram (660-pound) limit allowed under the deal, spokesman Fredrik Dahl said. 

Iranian Foreign Minister Mohammad Javad Zarif said the move was “reversible” but warned that Iran could continue to reduce its commitment to the agreement if Europe does not take action to uphold the other side of the deal, Iran’s official Islamic Republic News Agency reported. 

Exceeding the stockpile limit does not put Iran significantly closer to building a nuclear weapon, but it strikes another blow to the deal, which has been in jeopardy ever since the United States unilaterally withdrew last year. The low-enriched uranium, which is enriched to 3.67 percent, is suitable for use as fuel in nuclear power plants but is far short of the weapons-grade enrichment level of more than 90 percent needed for a nuclear bomb.

Iran has warned that it could undertake a more serious departure from the terms of the accord on July 7. Iranian officials have said they will move to enrich uranium to a higher level, coming a step closer to attaining weapons-grade material, if the remaining signatories to the accord do not provide sanctions relief by that deadline.

Iran has complained that it cannot reap the economic benefits promised under the nuclear accord because European companies are afraid of running afoul of sanctions reimposed by the United States after it pulled out of the pact.

“It’s been on life support for some time and is dying a slow death,” said Ali Ansari, a professor specializing in Iran at Britain’s St. Andrews University. While Iran will “keep pushing and keep pushing” for Europe to aid its economy, “it’s unclear what the Europeans can do.” The U.S. sanctions, combined with the “opaqueness” of the Iranian economy, make the country unattractive for many investors from Europe and elsewhere.

Ansari said he envisages only two ways out of the standoff: a conflict that “nobody wants” or a renegotiation of the nuclear deal. 

Iran’s decision to exceed the stockpile limit comes amid escalating tensions between Tehran and Washington. President Trump said late last month that he came close to authorizing strikes against Iran after it shot down an American surveillance drone over the Strait of Hormuz. The incident followed attacks on petrochemical tankers in the Gulf of Oman that the United States blamed on Iran, a charge Tehran denies. 

U.S. officials have previously suggested that they want Iran to remain within the limits of the nuclear deal — even though the Trump administration withdrew from it — saying U.S. sanctions do not give Iran an excuse to increase uranium production.

On Monday, the Trump administration went further, saying that Iran should not be allowed to enrich uranium at all. “It was a mistake under the Iran nuclear deal to allow Iran to enrich uranium at any level,” the White House said in a statement.

Henry Rome, an analyst at Eurasia Group, wrote that Iran is “the master of calibrated nuclear escalation. . . . It will likely push as far as it can without triggering a sanctions response from Europe or a military response from the U.S.”

Tehran wants to show that “it will not take U.S. pressure sitting down,” he continued, adding that the decision to exceed the stockpile limit is in line with other actions Iran and its allies have taken over the past two months, including the alleged rocketing of Iraqi bases and attacks on Saudi oil infrastructure. Iran also wants to prod Europe into taking more steps to ease its economic pressure, Rome said.

The remaining signatories to the deal, originally signed by six world powers and Iran, have been scrambling to keep the agreement alive since Trump pulled out. Germany, Britain and France have been working on a complex barter system that would allow European businesses to trade with Iran, but it is limited in scope, focusing on essential goods such as medicine and humanitarian items. 

As part of a last-ditch attempt to keep Iran in the deal, the European Union announced that the barter system was active after E.U. officials met with senior Iranian officials in Vienna on Friday. But no transaction has yet to be completed using the system.

Zarif said that two days after the United States withdrew from the accord, the Europeans made 11 commitments to keep it alive. Those included the continuing sale of Iranian oil on world markets and the return of frozen Iranian assets and oil-sale income, he said.

The barter system “does not satisfy any of the commitments,” Zarif said. Without fulfilling the commitments, he added, the trading system is “meaningless.”

European diplomats had been bracing for the Iranian announcement. Europeans view the breach as easily reversible and as a negotiating tactic to try to win additional concessions from the other parties to the nuclear deal, two European diplomats familiar with the discussions said. They spoke on the condition of anonymity to talk about the sensitive negotiations.

European countries have considered the nuclear deal essential for maintaining security in a volatile Middle East. Seven European nations released a statement Friday supporting the pact and calling it a “major contribution to stability.”

The Europeans are trying to hold the deal together and don’t want to be rushed into taking steps against Iran. But they say they may have no choice but to trigger clauses that could eventually lead to the reimposition of more sanctions — and a full breakdown of the agreement.

The steps Iran has taken are already making it more difficult for Europeans to get trade flowing through the barter system, called Instex, the diplomats said. The Europeans have been trying to show Tehran good will by going ahead with some transactions. But if Iran moves toward a more extensive breach of the deal on Sunday, it will become politically difficult to undertake transactions using Instex, one of the diplomats said.

Iranian Foreign Ministry spokesman Abbas Mousavi said that unless Europe took “practical and tangible steps” to make Instex operational before the Sunday deadline, Iran would take the “second step” toward reducing its commitment under the agreement: enriching uranium beyond the 3.67 percent level.

Iran has previously threatened to increase enrichment levels to 20 percent. That would still be less than the level required to manufacture a weapon but would reduce Iran’s “breakout time,” the amount of time needed to accumulate enough weapons-grade enriched uranium to make one nuclear bomb, experts say.

Before the nuclear deal, Iran’s breakout time was estimated to be about two or three months, according to the U.S.-based Arms Control Association. The group said the conditions in the accord increased that time to about a year

In announcing the decision to exceed the stockpile limit, Zarif cited  Article 36 of the accord, which lays out the process if any of the parties to the agreement, known officially as the Joint Comprehensive Plan of Action, think it is not being upheld. Iran has “triggered and exhausted” Article 36 since the U.S. withdrawal, Zarif tweeted. 

“Iran has stated that if sanctions are reinstated in whole or in part, Iran will treat that as grounds to cease performing its commitments under this JCPOA in whole or in part,” the article says. 

Israeli Prime Minister Benjamin Netanyahu, who campaigned against the nuclear deal and called for the United States to withdraw, criticized Iran on Monday for overstepping the 300-kilogram limit. He called on Europe to reimpose sanctions against Iran: “I say to you: Do it. Just do it.”

Birnbaum reported from Athens. Erin Cunningham in Istanbul contributed to this report.