LONDON — Iran has breached a crucial limit on the level of uranium enrichment set out in the 2015 nuclear deal, the country’s atomic energy agency said on Monday, as China, another signatory to the deal, accused the United States of “bullying” Tehran with crippling economic sanctions.
Behrouz Kamalvandi, a spokesman for Iran’s atomic energy agency, told the Iranian state broadcaster IRIB that the country had surpassed a limit of 3.67 percent uranium enrichment, and was prepared to go further.
Mr. Kamalvandi later told another Iranian news outlet, ISNA, that the enrichment level was above 4.5 percent.
He added that inspectors from the International Atomic Energy Agency, who have the task of monitoring Iran’s compliance with the limits set out in the deal, were expected to confirm that information on Monday. The agency did not immediately respond to a request for confirmation of the enrichment level.
The change moves Iran closer to — but still far short of — the level of uranium enrichment needed to produce nuclear weapons. But Iran has maintained that the higher enrichment level would be for peaceful purposes only.
The United States withdrew last year from the landmark nuclear accord with other powers and Iran, and reimposed punishing economic sanctions on the Middle Eastern country.
Iran has responded with a series of steps away from its obligations under the accord, which was intended to block Tehran from obtaining a nuclear weapon, in exchange for the lifting of sanctions.
A spokesman for the Chinese Foreign Ministry, Geng Shuang, called the American sanctions on Iran “bullying” in a news conference on Monday.
“The U.S. side not only unilaterally withdrew from the agreement but also created more and more obstacles for Iran and other parties to implement the agreement through unilateral sanctions and long-armed jurisdiction,” he said. “It has been proven that unilateral bullying has become a worsening ‘tumor’ and is creating more problems and greater crises on a global scale.”
European signatories to the nuclear agreement have found themselves in a difficult position, stuck between adhering to the American sanctions that target Iran’s oil industry and obligations to ease the economic burden on Iran under the nuclear deal.
Monday’s announcement came one day after Iran’s government spokesman, Ali Rabiei, said the country was just hours away from breaching the 3.67 percent limit on uranium enrichment. A week earlier, Iran announced it had exceeded another critical limit on how much nuclear fuel it could stockpile under the agreement.
Tehran has said that reducing its commitments under the deal is not a direct violation of the terms of the nuclear agreement, saying it is exercising its right to react to the United States’ walking away from the accord.
Mr. Rabiei posted on Twitter late on Sunday that the increase is “purely rooted in economic priorities.”
On Sunday, Iran also set a 60-day deadline for European signatories to come up with a strategy to ease the economic impact of the American sanctions, or Tehran would take further steps to walk back its obligations under the deal.
Less than 1 percent of naturally occurring uranium is U-235, a highly radioactive isotope, and enrichment means increasing that level. The 2015 agreement limited Iran to producing uranium that is no more than 3.67 percent U-235, a typical level of enrichment for use in a nuclear power plant.
Before the pact was signed, Iran had raised some of its uranium stockpile to 20 percent, which it said was needed for a research reactor. Atomic bombs use much more highly enriched uranium, generally over 80 percent.
Despite the increase in its uranium stockpile and its production of more highly enriched uranium, experts say Iran is still far from producing a nuclear weapon.
Separately, the Iranian defense minister, Amir Hatami, said in a speech broadcast Monday on state television that Britain’s seizure of an Iranian tanker near Gibraltar on Thursday would not be tolerated.
British and Gibraltar authorities said the tanker was transporting oil to Syria, and was detained because the delivery would violate the European Union’s sanctions on sales to that war-torn nation — not because it would violate American sanctions designed to choke off Iranian exports.
Speaking during a military ceremony, Mr. Hatami called the action a “provocative move” and said he would summon the British ambassador to account for the decision, according to the semiofficial state news outlet Mehr News.
“We will not put up with this act of marine piracy by the U.K.,” Mr. Hatami said, according to Mehr News.
A spokesman for the Iranian Foreign Ministry, Abbas Mousavi, said that the vessel had not been bound for Syria as British officials had suggested, Iranian state media reported.