Iran has taken steps to enrich uranium metal to a 20 percent purity and manufacture nuclear reactor fuel, the United Nation’s top nuclear watchdog announced Tuesday.

With the use of "indigenously-produced uranium" Iran will reportedly use fuel to supply the Tehran Research Reactor, but the U.S. and allied nations have called the move "worrying."

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State Department spokesperson Ned Price said it was "another unfortunate step backwards" as the U.S. has engaged in indirect talks on nuclear nonproliferation with Iran since April.

Price told reporters Tuesday that the move will not give Iran any leverage as the U.S. seeks to re-establish a nuclear agreement with the Middle Eastern nation, and said the "window for diplomacy remains open."

Under the Joint Comprehensive Plan of Action (JCPOA) -- which Donald Trump pulled the U.S. out of in 2018 -- Iran is not permitted to enrich uranium past a 3.67 percent purity threshold, which is all that is needed to power a commercial-grade power plant, according to the Arms Control Association.

But International Atomic Energy Agency (IAEA) Director-General Rafael Mariano Grossi said Tuesday that Iran had breached the regulation.

"Today, Iran informed the Agency that UO2 [uranium dioxide] enriched up to 20 percent U–235 would be shipped to the R&D laboratory at the Fuel Fabrication Plant in Esfahan, where it would be converted to UF4 [Uranium tetrafluoride] and then to uranium metal-enriched to 20% U–235, before using it to manufacture the fuel," an IAEA spokesman said in a statement to Fox News.

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Uranium-235 can be used to fuel nuclear power plants and nuclear reactors that run naval ships, according to the Centers for Disease Control and Prevention. But it can also be used for nuclear weapons – prompting concern from Western nations.

In a unified statement condemning Iran’s plan, foreign ministers from France, Germany, and the United Kingdom called the move "concerning" and an "escalation of its nuclear violations."

"Iran has no credible civilian need for uranium metal R&D and production, which are a key step in the development of a nuclear weapon," the group said.

"We strongly urge Iran to halt all activities in violation of the JCPoA, without delay and to return to the negotiations in Vienna with a view to bringing them to a swift conclusion," the foreign ministers continued. "Iran is threatening a successful outcome to the Vienna talks despite the progress achieved in six rounds of negotiations to date."

There are no set plans for direct talks between the U.S. and Iran.

Price said the U.S. is not pushing Iran on a hard deadline when it comes to the negotiating table but said the administration is continuing to assess the situation.

Professor Eyal Zisser of Tel-Aviv University and former head of the Moshe Dayan Center for Middle Eastern and African Studies told Fox News this announcement "is part of the Iranian game to put pressure on the United States and to get a better deal."

Zisser explained that the Iranians can feel how much Washington wants the deal, so they are adding pressure and creating a crisis to get a better deal.