US President Donald Trump has withdrawn the US from the landmark nuclear accord with Iran.
Mr Trump pledged to works with America's allies to curb the threat from Iran. He said he will reinstate the "highest possible sanctions" on Iran.
He described the agreement, struck during the Obama administration, as "decaying and rotten".
Mr Trump described Iran as the world's leading state sponsors of terrorism.
The president spoke out against the arrangement as "a horrible, one-sided deal" based on a lie.
He said that if he allowed the deal to stand, there would soon be a nuclear arms race.
He called Iran a "regime of great terror".
And he said that "no action taken by the regime has been more dangerous than its pursuit of nuclear weapons and the means of delivering them".
He said he was ready and willing to negotiate a new deal when Iran was ready.
Mr Trump said America "will not be held hostage to nuclear blackmail" and will not allow "a regime that chants 'Death to America'" to get access to nuclear weapons.
The president said he made the decision after consulting with US allies.
The move would deal a profound blow to US allies and potentially deepen the president’s isolation on the world stage.
It was not immediately clear which sanctions that were lifted under the deal might be quickly reimposed, said the sources, who were not authorised to speak publicly.
I will be announcing my decision on the Iran Deal tomorrow from the White House at 2:00pm.— Donald J. Trump (@realDonaldTrump) May 7, 2018
In a burst of last-minute diplomacy, punctuated by a visit by UK Foreign Secretary Boris Johnson, the deal’s European members gave in to many of Mr Trump’s demands, according to officials, diplomats and others briefed on the negotiations.
Yet they still left convinced he was likely to re-impose sanctions and walk away from the deal he has lambasted since his days as a presidential candidate.
The agreement, struck in 2015 by the United States, other world powers and Iran, lifted most US and international sanctions against the country. In return, Iran agreed to restrictions on its nuclear programme making it impossible to produce a bomb, along with rigorous inspections.
Mr Trump spoke with French President Emmanuel Macron and Chinese leader Xi Jinping about his decision on Tuesday. Mr Macron’s office said the two spoke about “peace and stability in the Mideast,” without elaborating.
Mr Macron vigorously supports the deal and tried to persuade Mr Trump to stay committed to it during a visit to Washington last month.
Hours before the announcement, European countries involved in the agreement met to underline their support for it. Senior officials from Britain, France and Germany met in Brussels with Iran’s Deputy Foreign Minister for Political Affairs, Abbas Araghchi.
Building up anticipation, Mr Trump announced on Twitter he would disclose his decision at 2pm (7pm UK time) at the White House. With uncharacteristic discipline, he kept the decision confined to a small group within his National Security Council.
In Iran, many were deeply concerned about how Mr Trump’s decision could affect the already struggling economy. In Tehran, President Hassan Rouhani sought to calm nerves, smiling as he appeared at a petroleum expo. He did not name Mr Trump directly, but emphasised that Iran continued to seek “engagement with the world”.
“It is possible that we will face some problems for two or three months, but we will pass through this,” Mr Rouhani said.