In increasingly intense rhetorical terms, U.S. officials insisted they had acted legitimately in triggering a so-called “snapback” mechanism that would re-impose all U.N. sanctions Iran next month. They said the re-imposition of sanctions is a done deal and nothing can stop it.

“Last week, the U.S. triggered the 30-day process to restore virtually all UN sanctions on Iran after the Security Council failed to uphold its mission to maintain international peace and security,” Secretary of State Mike Pompeo said in a tweet. “These sanctions will snap back at midnight GMT on September 20.”

But as they did when Pompeo traveled to the U.N. to invoke snapback, almost all other council members flatly rejected that position, repeating their position that the U.S. had lost its legal standing to act after President Donald Trump withdrew from the 2015 Iran nuclear deal two years ago.

At the heart of the dispute is the Security Council resolution that endorsed the Joint Comprehensive Plan of Action, or JCPOA, between Iran and six major powers — the U.S., Russia, China, United Kingdom, France and Germany.

It allows “a JCPOA participant state” to trigger the “snapback” mechanism. The U.S. insists that as an original JCPOA participant it has the legal right even though it ceased participating in 2018.

The impasse sets the stage for a potential crisis in the Security Council next month with the United States claiming to have re-imposed the sanctions and most of the rest of the world saying the Trump administration’s action is illegal and ignoring it.

The president of the council on Tuesday said there was overwhelming opposition in the 15-member body to the U.S. position and that it was unlikely there would be any action on Washington’s demand.

But Pompeo said that wouldn’t matter, citing the process for sanctions re-imposition outlined in council resolution that enshrined the nuclear deal. Under the terms of that resolution, if a participant in the deal accuses Iran of “significant non-performance,” the council must vote affirmatively to continue sanctions relief. The U.S. would veto any such resolution.

“If any member of the UN Security Council introduces a resolution to continue sanctions relief, the U.S. will oppose it,” Pompeo said. “If no resolution is introduced, the sanctions on Iran will still return on September 20. That’s how UNSCR 2231 works.”

The European Union’s foreign policy chief, who coordinates the JCPOA’s Joint Commission, reiterated in response to Pompeo’s latest statement that since the U.S. withdrew from the agreement in 2018 “it cannot ... be considered to be a JCPOA participant state for the purposes of possible sanctions snapback foreseen by the resolution.”

EU High Representative Josep Borrell added that he “will continue to do everything possible to ensure the preservation and full implementation of the JCPOA by all,” saying it remains “a key pillar” of global nonproliferation that contributes to regional stability.

The EU announced last Friday that the six remaining parties to the JCPOA will meet in Vienna on Sept. 1.

Russia’s deputy U.N. ambassador Dmitry Polyansky tweeted Thursday: “Under intl law you can’t withdraw from an agreement and then claim you can still benefit from its provisions. Under `rules-based intl order’ where the rules are defined by the US this seems to be OK provided it serves US interests.”

The Trump administration has been waging war on the nuclear deal for years. During the 2016 presidential campaign candidate Trump denounced it as the worst deal ever negotiated and has made no secret of his desire to blow it up. U.S. officials say the deal is fatally flawed because certain restrictions on Iran's nuclear activity gradually expire and will allow the country to eventually develop atomic weapons.

JCPOA supporters warn that if the deal blows up or Iran pulls out it could pursue nuclear weapons.

Pompeo came to the United Nations last week to demand restoration of U.N. sanctions after the Security Council resoundingly rejected a U.S. resolution to indefinitely extend the U.N. arms embargo on Iran, which is set to expire Oct. 18, in one of the first restrictions to be lifted. Only the Dominican Republic supported the United States.

Former Trump national security adviser John Bolton, who has long questioned the validity of the administration’s argument for snapback, told The Associated Press: “The lesson you take away from this is for the United States it’s perfectly honorable to stand alone at the U.N. in vindication of our principles. But at least you ought to try and do it smartly, and not so that you look foolish.”

“I think we look foolish,” he said. “And what we’re going to see here is what happens when you get into this kind of foolishness. It really is too cute by half and now it is coming back to bite the United States, and it was entirely predictable.”