President Trump suffered a setback in his efforts to persuade allies to abandon the Iran nuclear deal once and for all when British Prime Minister Boris Johnson signaled that the United Kingdom remains committed to the agreement.

Johnson has positioned himself as a close partner of Washington and backed Trump’s decision to launch the drone strike that killed Iran’s most powerful military leader. On Thursday, he spoke to Hassan Rouhani, the Iranian president, to demand an end to further military retaliation.

“They discussed the situation in the region following the death of Qassem Soleimani, and the prime minister called for an end to hostilities,” said a spokesman for No. 10 Downing St.

Johnson also "underlined the U.K. commitment to the [Joint Comprehensive Plan of Action] and to ongoing dialogue to avoid nuclear proliferation and reduce tension," the spokesman said.

The statement puts the U.K. at odds with the United States at a crucial time for the Middle East.

A day earlier, Trump claimed that sanctions lifted under the terms of the deal had freed money for a “terror spree” and paid for the missiles fired on Iraqi bases on Tuesday night. He demanded that the other signatories, including Germany, France, Russia, and China, recognized that “reality.”

“They must now break away from the remnants of the Iran deal — or JCPOA — and we must all work together toward making a deal with Iran that makes the world a safer and more peaceful place,” he said.

The Iran deal was finalized in 2015, lifting a raft of sanctions after Tehran agreed to restrict sensitive nuclear activities and allow in inspectors. In 2018, Trump withdrew the U.S. from the deal and reimposed sanctions amid growing concerns about Iran’s missile tests and its support for militant groups across the Middle East.

Last year, Iran said it would no longer abide by the terms and would resume production of highly enriched uranium.

Trump has repeatedly called for a new Iran deal that would not only limit Tehran’s ability to pursue nuclear weapons but also restrict its aggressive posture. The 2015 agreement was devised narrowly as an anti-proliferation treaty, saying nothing about Iran's conventional missile program or its sponsorship of armed groups such as Hezbollah.

However, his European counterparts say they see things differently.

British officials say they want to see Iran fall back into line with the terms of the deal and will use the existing mechanisms within the 2015 agreement to do so. Its dispute resolution mechanism allows the U.K. to reimpose sanctions if Iran is found to have breached the terms of the deal.

U.K. foreign secretary Dominic Raab visited Washington this week and said Britain was “looking at all measures” when it comes to the deal.

Privately, officials say the deal is slipping toward irrelevance and that Trump’s stance has backfired.

“Iran has begun real progress towards nuclearization again, and the U.S. has so far got nothing in return,” said one. “Which was what we said would happen all along.”

For now, however, he said they remain committed to working within the terms of the deal, which means Trump may struggle to find partners willing to pursue a new strategy.

Last weekend, France and Germany joined with the U.K. to urge Iran to stick to the deal.

Vice President Mike Pence said on Thursday that the White House would be calling on world leaders in the near future.

"The president is going to call on our allies in the days ahead to join the U.S. to withdraw from the disastrous Iran nuclear deal and demand that Iran abandon its long history of sowing terrorist violence, abandon its nuclear ambitions and join the family of nations," he said during an interview on Fox & Friends.

