US President Donald Trump has announced he is pulling out of the Iran nuclear deal.
Here we look at the background to the controversial decision:
What is the Iran nuclear deal?
-- Foreign Office ?? (@foreignoffice) July 14, 2016
Iran agreed to rein in its nuclear programme in a 2015 deal struck with the US, UK, Russia, China, France and Germany.
Under the Joint Comprehensive Plan of Action (JCPOA) Tehran agreed to significantly cut its stores of centrifuges, enriched uranium and heavy-water, all key components for nuclear weapons.
Why did Iran agree to the deal?
It had been hit with devastating economic sanctions by the United Nations, United States and the European Union that are estimated to have cost it tens of billions of pounds a year in lost oil export revenues. Billions in overseas assets had also been frozen.
Why is it under threat?
Iran is failing at every level despite the terrible deal made with them by the Obama Administration. The great Iranian people have been repressed for many years. They are hungry for food & for freedom. Along with human rights, the wealth of Iran is being looted. TIME FOR CHANGE!
-- Donald J. Trump (@realDonaldTrump) January 1, 2018
The deal was the key foreign policy achievement of Barack Obama's presidency, making it an immediate target for successor Donald Trump.
On the presidential campaign trail Mr Trump made his opposition clear and then continued to make threats about pulling out of the "worst" deal the US has "ever" signed up to because of its "disastrous flaws".
The next deadline in the US for waiving sanctions is May 12 but Mr Trump announced on Monday that he would reveal his decision today.
What is Britain's position?
-- The Iran Deal (NARA) (@TheIranDeal) July 14, 2016
The Government does admit the deal is not perfect as it fails to cover areas such as ballistic missiles and is time-limited, but insists it is the option with the "fewest disadvantages".
Germany, France and the United Nations all urged the US not to withdraw, with Foreign Secretary Boris Johnson making a last-ditch attempt to preserve the deal during a trip to Washington on Monday.
What happens now the United States has pulled out?
Iran has warned the move effectively amounts to "killing the deal".