President Donald Trump has said that Iran is "playing with fire" after Tehran announced it had exceeded its limit for low-enriched uranium allowed under a 2015 nuclear deal with world powers.
"They know what they're doing. They know what they're playing with and I think they're playing with fire," Trump told reporters at the White House when asked if he had a message for Iran.
In Tehran, Iranian Foreign Minister Javad Zarif expressed exasperation over a White House statement that said there was "little doubt that even before the deal's existence, Iran was violating its terms."
Replying to the July 1 White House statement, Zarif wrote on Twitter, "Seriously?"
The United States withdrew from the nuclear deal in 2018 and reimposed sanctions on Iran's oil exports and other sectors.
Tehran has sought to pressure the remaining parties to save the deal, but announced on May 8 it would no longer respect the limit set on its enriched-uranium and heavy-water stockpiles.
U.S. Secretary of State Mike Pompeo called on July 1 for Iran to halt all uranium enrichment, saying "no nuclear deal should ever allow the Iranian regime to enrich uranium at any level."
"The United States is committed to negotiating a new and comprehensive deal with the Iranian regime to resolve its threats to international peace and security, " Pompeo said in a statement. "As long as Iran continues to reject diplomacy and expand its nuclear program, the economic pressure and diplomatic isolation will intensify."
"The Trump administration calls on the international community to restore the long-standing nonproliferation standard of no enrichment for Iran's nuclear program," Pompeo said. "Iran has the uncontested ability to pursue peaceful nuclear energy without domestic enrichment."
Earlier on July 1, the International Atomic Energy Agency (IAEA) verified Iran's claim that it had exceeded the low-enriched-uranium limit in response to the U.S. withdrawal from the 2015 nuclear deal.
IAEA Director-General Yukiya Amano informed the UN nuclear watchdog's board of governors of the development in Vienna on July 1.
Iran's state-run IRNA news agency earlier the same day quoted Zarif as acknowledging to journalists that the 300-kilogram limit had been breached, adding that Iran considered it "our right reserved in the nuclear deal."
The comment came after the semiofficial Fars news agency quoted a source as saying that IAEA inspectors had measured the stockpile and confirmed it had surpassed the cap.
The UN watchdog is expected to file a report on the issue.
The terms of the 2015 nuclear accord limit the enrichment and stockpiles of Iran's uranium, and reduce the country’s nuclear capabilities in return for relief from international sanctions.
But the United States unilaterally abandoned the pact in May 2018 and later reimposed sanctions on Iran that had been lifted under the deal.
Iranian officials have complained that the remaining parties to the deal -- Britain, France, Germany, China, and Russia -- have failed to mitigate the effects of the U.S. sanctions on Iran's economy.
Tehran has set a July 7 deadline for those countries to offer relief from the sanctions before it begins enriching uranium beyond 3.67 percent concentration.
Before the nuclear deal, Iran had enriched uranium to as high as 20 percent, putting weapons-grade levels within reach.
IRNA quoted Foreign Minister Zarif as saying that "if Europeans do what they have to do, our measures are reversible."
He was quoted by AP as saying that if Europe did not take steps to save the accord, "the next step is about the 3.67 percent limitation, which we will implement, too."
European countries have warned that any violation of the agreement, which aimed at heading off any pathway to Iran developing nuclear weapons, would bring consequences, but did not say what they might be.
British Foreign Secretary Jeremy Hunt tweeted that he was "deeply worried" by Iran's announcement.
Prime Minister Theresa May's spokesman, James Slack, said that Iran's announcement was "extremely concerning," but said Britain would continue to work with the remaining parties of the deal -- particularly Germany and France -- to keep the nuclear deal in place.
"We have been consistently clear that our commitment to the JCPOA depends on Iran complying in full with the terms of the deal and we urge them to reverse this step," Slack said.
Enriched uranium is used to make reactor fuel and, enriched at higher levels, could be used to make nuclear weapons.
Relations between Washington and Tehran have plummeted since the U.S. pullout of the nuclear deal, with recent attacks on oil tankers in the Gulf of Oman and near the Strait of Hormuz exacerbating the situation.
Washington has blamed Iran for the incidents, while Tehran denied any involvement.
In a speech on July 1, Iran's Zarif said that Iran "will never yield to pressure from the United States."
"Today, Iran has to stand against U.S. economic sanctions through domestic production and relying on national potentials," Zarif said, without mentioning the country's nuclear program.
In announcing the U.S. withdrawal from the Iran accord, President Donald Trump argued that the terms were not tough enough to prevent Iran from developing nuclear weapons and did not address the country's missile program or its support for militants in the region.
Iran has denied it supports militant activity and said its nuclear program is strictly for civilian energy purposes.
Russian Deputy Foreign Minister Sergei Ryabkov on July 1 said it was "regrettable" that the 300-kilogram limit had been exceeded, but said the development should not be overdramatized, according to the state-run news agency TASS.
Interfax quoted Ryabkov as saying the breach did not come as a surprise, and urged Iran to take a responsible approach toward implementing the safeguards agreement with the IAEA under the nuclear deal.