America's new Secretary of State John Kerry is holding talks with the Prime Minister and Foreign Secretary William Hague on the first stop in an 11-day 'listening tour' that will take him to Paris, Rome and Cairo among other cities.
US Secretary of State John Kerry said Iran still had time to find a diplomatic solution to the standoff over its nuclear programme but added that they must negotiate with world powers in good faith.
The window for a diplomatic solution simply cannot by definition remain open forever. But it is open today. It is open now.
There is still time but there is only time if Iran makes the decision to come to the table and negotiate in good faith. We are prepared to negotiate in good faith, in mutual respect in an effort to avoid whatever terrible consequences could follow failure. And so the choice really is in the hands of the Iranians. And we hope they will make the right choice.
John Kerry has spoken of the "remarkable relationship" between the UK and US on his first foreign visit since becoming the US Secretary of State.
He said the two countries "stood together time and time again to meet the world's great challenges" and reiterated Barack Obama and David Cameron's description of the relationship as a "partnership of the heart."
Mr Kerry is on an 11-day "listening tour" that will see him travel to cities including Paris and Cairo.