Donald Trump's refusal to formally certify the Iran deal will have profound consequences for trust in the US, Labour MPs have said.
Shadow first secretary of state Emily Thornberry called on the UK government to "stand up" to the 45th President of the United States, telling the House of Commons this afternoon it was "behaviour we have come to expect" of him.
Thornberry said the deal was "working", preventing "what could have been another North Korea in the Middle East".
She added: "It puts us in the position that we will never feel secure doing a deal with America again."
Labour colleague Hilary Benn concurred, adding: "This is an agreement not based on trust, it is an agreement based on distrust. [Pulling out] will enable the less than moderate forces in Iran to say to more moderate forces 'we told you, you can't trust the US'."
Mike Gapes noted that the repercussions will stretch beyond the Middle East, adding Trump's actions made it "almost impossible" to reach a compromise with an increasingly aggressive North Korea.
Trump announced his decision not to re-certify the deal, originally agreed in 2015, late on Friday night. The deal, which was signed by Britain, China, France, Russia, Germany and the European Union, must be re-certified by the US every 90 days.
In a rare move, Prime Minister Theresa May, German Chancellor Angela Merkel and French President Emmanuel Macron issued a joint statement confirming their commitment to the plan "and its full implementation by all sides".
They also said they were "concerned by the possible implications", although stopped short of a full-blown condemnation.