British Foreign Secretary Boris Johnson will on Sunday begin a two-day visit to Washington, with the Iran nuclear deal, Syria and North Korea on top of the agenda, the Foreign Office said.
Johnson will meet US Vice President Mike Pence, National Security Advisor John Bolton and Congressional foreign policy leaders.
"On so many of the world's foreign policy challenges the UK and US are in lockstep," said Johnson, highlighting the joint responses to Russian provocations, North Korea and Syria.
"The UK, US, and European partners are also united in our effort to tackle the kind of Iranian behaviour that makes the Middle East region less secure -- its cyber activities, its support for groups like Hezbollah, and its dangerous missile programme," he added.
Britain remains committed the nuclear deal Iran signed with world powers in 2015, but US President Donald Trump has threatened to abandon the agreement when it comes up for renewal on May 12, calling it "insane".
Britain, France and Germany -- the three European countries that signed the deal -- have repeatedly tried to persuade Trump not to abandon it.