The U.N. nuclear watchdog harshly criticized Iran on Saturday for effectively barring several of its most experienced inspectors from monitoring the country’s disputed atomic program.

The strongly worded statement came amid longstanding tensions between Iran and the International Atomic Energy Agency, which is tasked with monitoring a nuclear program that Western nations have long suspected is aimed at eventually developing a nuclear weapon. Iran insists the program is peaceful.

Rafael Mariano Grossi, the head of the IAEA, said Iran had withdrawn the designation of “several experienced Agency inspectors,” barring them from taking part in the monitoring of its program.

“Iran has effectively removed about one-third of the core group of the agency’s most experienced inspectors designated for Iran,” he said.

Grossi went on to “strongly condemn this disproportionate and unprecedented unilateral measure,” saying it “constitutes an unnecessary blow to an already strained relationship between the IAEA and Iran.”

Iran’s Foreign Ministry linked the move to what it said was an attempt by the United States and three European countries to misuse the IAEA “for their own political purposes.”

The U.S., Britain, France and Germany criticized Iran in a joint statement at an IAEA board meeting in Vienna this week, calling on Tehran to step up cooperation with the agency.

Britain, France and Germany also said Thursday that they would maintain sanctions on Iran related to its nuclear and ballistic missile programs.

“Iran had previously warned about the consequences of such political abuses, including the attempt to politicize the atmosphere of the agency,” said Nasser Kanaani, spokesman for Iran’s Foreign Ministry.

The Vienna-based IAEA reported earlier this month that Iran had slowed the pace at which it is enriching uranium to nearly weapons-grade levels. That was seen as a sign that Tehran was trying to ease tensions after years of strain between it and the U.S.

Iran and the U.S. are negotiating a prisoner swap and the release of billions of dollars in Iranian assets frozen in South Korea.

World powers struck a deal with Tehran in 2015 under which it agreed to limit enrichment of uranium to levels necessary for nuclear power in exchange for the lifting of economic sanctions. U.N. inspectors were tasked with monitoring the program.

Then-President Donald Trump unilaterally pulled the U.S. out of the accord in 2018, restoring crippling sanctions. Iran began breaking the terms a year later. Formal talks in Vienna to try to restart the deal collapsed in August 2022.

Iran has long denied ever seeking nuclear weapons and continues to insist that its program is entirely for peaceful purposes, though Grossi has warned that Tehran has enough enriched uranium for “several” nuclear bombs if it chose to build them.

Tehran likely would still need months to build a weapon.

The IAEA, the West and other countries say Iran had a secret military nuclear program it abandoned in 2003.

“Without effective cooperation, confidence and trust will continue to be elusive,” Grossi said Saturday. Without these inspectors, he said, the agency will not be able to effectively “provide credible assurances that nuclear material and activities in Iran are for peaceful purposes.”

(AP)