Boris Johnson, the foreign secretary, is travelling to the United States as part of a last-ditch diplomatic effort to persuade Donald Trump not to scrap the Iran nuclear deal.
The US president has fiercely criticised the agreement, which eased sanctions on Tehran in exchange for commitments to abandon its nuclear weapons programme.
Mr Trump will decide on May 12 whether to reimpose sanctions and effectively torpedo the international alliance behind the deal.
The Foreign Secretary will travel to Washington on Sunday for two days of talks with senior administration officials including vice president Mike Pence.
He will also meet national security adviser John Bolton and key foreign policy leaders...