All sanctions against Iran that were suspended under the 2015 nuclear deal will resume in 31 days under a process Secretary of State Mike Pompeo started Thursday, in a move that is exposing deep divisions between the United States and other countries on the U.N. Security Council and could spell the death of the landmark agreement.

Pompeo filed an official complaint with the president of the Security Council, accusing Iran of violating the 2015 nuclear deal, which President Trump withdrew from two years ago. Under the agreement, that means sanctions will be “snapped back” into place next month unless the Security Council votes to keep them lifted — a move certain to trigger a U.S. veto.

The process includes an extension of an arms embargo due to expire in mid-October. A U.S. proposal to keep it in place was roundly defeated in a Security Council vote last week in which only the Dominican Republic sided with the United States.

“Our message is very, very simple,” Pompeo told reporters after meeting with the Security Council’s president and U.N. Secretary General António Guterres. “The United States will never allow the world’s largest state sponsor of terrorism to freely buy and sell planes, tanks, missiles and other kinds of conventional weapons.”

The U.S. action, though long expected, drew sharp condemnation from Russia and the three European countries that were partners in negotiating the agreement, which lifted all sanctions against Iran in return for limits on its nuclear program.

France, Germany and Britain issued a statement questioning the authority of the United States to demand a snapback since it is no longer a participant in the agreement, which is known officially as the Joint Comprehensive Plan of Action.

The countries noted that the United States “ceased to be a participant to the JCPOA following their withdrawal from the deal on May 8, 2018,” said the statement, which was issued in the name of the countries’ foreign ministers. “We cannot therefore support this action which is incompatible with our current efforts to support the JCPOA.”

They warned that the U.S. effort could undermine the U.N. Security Council.

“We remain guided by the objective of upholding the authority and integrity of the United Nations Security Council,” the statement said. “We call on all UNSC members to refrain from any action that would only deepen divisions in the Security Council or that would have serious adverse consequences on its work.”

The European Union’s foreign policy chief, Josep Borrell, said the unilateral U.S. withdrawal from the agreement means it cannot initiate snapback. “I will continue to do everything possible to ensure the preservation and full implementation of the JCPOA by all,” he said in a statement, calling the agreement a pillar of nonproliferation and regional security.

Russia’s U.N. ambassador, Vassily Nebenzia, dismissed the U.S. move as “nonexistent,” saying only a country that is still in the deal can legitimately trigger a snapback.

“He’s not triggering a snapback,” Nebenzia said of Pompeo, even before he arrived in New York. “Snapback can be triggered by a country that is a participant of the JCPOA, which the U.S. is not.”

The U.S. decision to start the process toward the snapback of sanctions suspended almost five years ago now enters a murky phase. China and Russia, also signatories to the agreement, oppose the resumption of sanctions and want to sell weapons to Iran. The Europeans share many of the U.S. concerns over Iran’s interference in neighboring countries. The JCPOA has been hanging by a thread since the Trump administration began reapplying a stream of U.S. sanctions, but the Europeans want to keep the deal alive.

The U.S. allies, several of whose officials spoke on the condition of anonymity out of what they said was a rapidly deepening Council divide, were taken aback at Pompeo’s description of them, in his U.N. news conference, as siding with Iran’s “ayatollahs” and privately thanking the administration for Thursday’s action.

“We understand the views on Iran,” said one European official. “But ultimately we take a different view on their ability to trigger snap-back.” While acknowledging that the text of the resolution was not clearly written, this official and others said that it was clear to all that it was composed to deal with an Iranian withdrawal from the agreement, not for the withdrawal of one of the Western signatories. European reaction ranged from irritated to infuriated, while “Russia and China want to be talking about this as much as possible,” the official said.

There is allied agreement that removing the conventional weapons embargo is a bad thing, although the Europeans say they are more concerned that Iran will use the situation to further enhance its nuclear capabilities than to buy more conventional weapons. Russia and China already flout U.S. sanctions regularly.

Europeans had made what they said were strenuous efforts in recent weeks to persuade both Moscow and Beijing to agree to extend the embargo. Those efforts, officials said, were ultimately undercut by U.S. rhetoric and insistence that only the snap back of all sanctions against Iran would suffice, and that it had the unilateral right to demand them.

Pompeo made clear that once the suspended sanctions return, the United States will go after any nation that violates them, whether friend or foe.

“We will continue to enforce the sanctions after these U.N. Security Council resolutions come back in place,” Pompeo said. “The country is immaterial. If there’s a violation of the sanctions, we’ll do our level best to enforce them.”

Except for a few allies, the United States is largely alone in its contention that it still has the authority to trigger snapback sanctions. The argument stems from a State Department legal opinion that any country that was a “participant state” in the original agreement has the right to trigger snapback even if it no longer is a participant in the deal.

“That right endures regardless of whether one views the United States as being in non-performance of the commitments it made under the JCPOA or as not currently participating in that political arrangement,” the legal opinion said.

Pompeo said Thursday that the Security Council could have inserted language that excludes dropout nations from triggering sanctions. But it didn’t, he said, and so the United States is still listed as a participant in the U.N. resolution that endorsed the deal and lifted U.N. sanctions.

Pompeo started the procedure with a letter to Indonesia’s U.N. ambassador, Dian Triansyah Djani, who is president of the Security Council this month. Pompeo wrote that Iran had exceeded its limits under the agreement for uranium enrichment and heavy water production, as well as research on advanced centrifuges. He wrote that “exhaustive diplomacy” with Iran by the European countries that co-signed the pact with the United States — Britain, France and Germany — had failed.

“The United States is therefore left with no choice but to notify the Council that Iran is in significant non-performance of its JCPOA commitments,” the letter states.

Now that the United States has started the procedure for returning to a pre-2015 set of sanctions against Iran, one of the big questions is whether Tehran will walk away from the JCPOA as Trump did.

Since the United States withdrew and began reimposing its own sanctions, Iran has gradually been ramping up its nuclear and ballistic missile programs. It has exceeded some limits prescribed in the agreement, but it has not given up on a deal Iranian President Hassan Rouhani has characterized as “half alive,” and it continues to allow inspectors from the International Atomic Energy Agency to monitor its activities. Numerous Iranian officials have said that invoking snapback sanctions would signal the death of the agreement.

In an ominous sign of a potential escalation in the confrontation between Tehran and Washington, Iran on Thursday unveiled two medium-range missiles, including one named after Iranian General Qasem Soleimani, whom Trump ordered killed in January.

Pompeo’s plan to set into motion the eventual resumption of sanctions was heavily advertised ahead of time. He has been threatening to do so since the spring, and Trump announced Wednesday that he had ordered Pompeo to go to the United Nations to start the process.

Michael Birnbaum contributed to this report.