"Today's announcement from Tehran is, I have to say to the House, an unwelcome step. We urge Iran not to take further escalatory steps and to stand by its commitments," Foreign Office minister Mark Field told parliament.

Prime Minister Theresa May's spokesman later told reporters: "We are extremely concerned about this announcement."

"This deal is a crucial agreement which makes the world safer and we will ensure it remains in place for as long as Iran upholds these commitments," he said.

The spokesman said Britain would hold talks with its partners, particularly France and Germany, over next steps.

Field said: "We are not at this stage talking about re-imposing sanctions, but one has to remember that they were, of course, lifted in exchange for the nuclear restrictions as part of that JCPOA (Joint Comprehensive Plan of Action)."

But he added: "Should Iran cease meeting its nuclear commitments, there would of course be consequences".