European powers referred Iran to the United Nations to face the reimposition of tough international sanctions after the Islamic Republic failed to comply with demands to negotiate with the U.S. and allow nuclear inspectors to resume their work.

The U.K., Germany and France on Thursday triggered a 30-day "snapback” process that would lead to a resumption of sanctions originally lifted as part of a 2015 deal, according to a U.K. official and a joint letter from what is known as the E3 nations addressed to the U.N. Security Council.

The move is likely to raise tensions between Tehran and the West amid an uneasy standoff over Iran’s atomic activities following Israeli and U.S. airstrikes on its key nuclear sites in June.

The decision came after a series of meetings between Iran and European and International Atomic Energy Agency officials this week, during which Tehran made clear it isn’t prepared to budge until its own conditions are met.

"Based on clear factual evidence, the E3 believe Iran to be in significant non-performance of its commitments under the JCPOA, and hereby invoke the process known as the ‘snapback’ mechanism,” the E3 said in the letter, referring to the official name of the 2015 agreement that saw Tehran curb its nuclear activity in exchange for sanctions relief.

Iran’s Foreign Minister Abbas Araghchi criticized the move as "unjustified, illegal and without any legal basis,” in a phone call with his British, French, German and EU counterparts during which they notified him of their decision, according to the state-run Islamic Republic News Agency.

Iran has threatened to leave the international Treaty on the Non-Proliferation of Nuclear Weapons if U.N. sanctions are resumed. That could permanently throttle IAEA inspections, creating deeper ambiguity over the nature and purpose of Iran’s atomic activities.

The U.S. welcomed the European plan, according to a statement from the State Department, adding that it remains open to "direct engagement with Iran” to seek a "peaceful, enduring resolution.”

A point of major concern for both the IAEA and the E3 is the state and whereabouts of Iran’s large quantity of near-bomb grade uranium, which hasn’t been verified in some 75 days.

"We are not yet where I would like us to be, I will not hide this,” IAEA Director General Rafael Mariano Grossi said Wednesday in Washington, between meetings with U.S. Secretary of State Marco Rubio and Special Envoy Steve Witkoff.

Iran has for years denied its nuclear program is for military purposes and both IAEA inspectors and U.S. intelligence communities have confirmed the absence of a weapons program in the country since the early 2000s.

Satellite images after the Israeli and U.S. strikes confirmed they destroyed large portions of an above-ground complex and also resulted in chemical and radiological hazards, which Iran says prevent the resumption of IAEA monitoring.

Tehran has rejected reentering negotiations with the U.S. as long as the Islamic Republic is at risk of further military attack. Iran is also seeking compensation for the June strikes and recognition of its right to enrich uranium.

The Europeans are acting now because their right to reimpose U.N. sanctions is due to expire on Oct. 18. The process — embedded in the original 2015 Iran deal which U.S. President Donald Trump abandoned during his first term — requires 30 days to complete.

The E3 is concerned about Iran’s noncompliance with the IAEA, which requires access to all Iran’s sites and nuclear material, as well as its unaccounted stock of highly enriched uranium at 60%, far above the 3.67% level of enrichment agreed within the 2015 deal, the U.K. official said.

E3 nations have sought to resolve the diplomatic crisis, but feel Iran has not seriously engaged with them, the U.S. or the IAEA, the official said. They remain committed to finding a diplomatic solution during the 30-day negotiation process.

What's known as the snapback mechanism would reapply U.N. sanctions that require Iran to suspend uranium enrichment, restrict its ballistic-missile program and imposed an arms embargo. Their resumption would also trigger the EU to re-instate its own sanctions targeting Iran’s oil and gas industry.

"In the next 30 days, there is a window of opportunity to avoid any further escalation and find a way forward that serves peace,” Stephane Dujarric, spokesperson for United Nations Secretary — General Antonio Guterres told reporters.

The U.N. chief "also underscores the imperative to exert all efforts to prevent a renewed military conflict, and calls for prioritizing dialog to address concerns related to Iran’s nuclear program and broader regional security,” Dujarric added.

Europe’s move has been fiercely resisted by China and Russia, who are lining up with Iran to argue the effort itself is a violation of the 2015 accord, suggesting that even if U.N. sanctions are reinstated, they may not be as widely observed as they were a decade ago.