President Trump withdraws from the Iran nuclear deal, calling it "decaying" and "defective at its core"
Trump signs a memorandum to immediately begin imposing economic sanctions on Iran lifted under the deal
The 2015 Obama-era pact restricts Iran's nuclear capabilities in exchange for lifting economic sanctions
Companies doing business in Iran will be allowed up to 180 days to end contracts or face "severe consequences"
That's all for our live coverage on reaction to today's announcement on the US withdrawal from the 2015 Iran nuclear deal.
Follow more updates on the BBC News website.
Jonathan Marcus
BBC Diplomatic and defence correspondent
Some fear that Trump may have brought a new and catastrophic regional war in the Middle East that much closer.
An imperfect deal that was working
The deal was not perfect. It did not cover a range of worrying Iranian activities from its missile programme to its regional behaviour. At worst you could say that it simply delayed a potential crisis.
The inconvenient truth for Donald Trump is that, as far as it goes, the nuclear deal was working.
Dangerous path ahead
A battle will now be under way in Tehran, and who wins out will determine if the agreement can be saved.
Even those who agree with Mr Trump's actions are left with fundamental questions to answer.
Where is the "Plan B"? How is Iran now to be contained?
Image source, Getty ImagesFormer Vice-President Joe Biden called Trump's decision "a profound mistake", saying it will only isolate the US while allowing Iran to gain "international sympathy while doing nothing to reduce its harmful activities".
Biden cautioned that the "unnecessary crisis" could lead to war with Iran.
"Talk of a 'better deal' is an illusion. It took years of sanctions pressure, painstaking diplomacy, and the full support of the international community to achieve that goal. We have none of that in place today."
"President Trump’s decision will do the opposite of what he says he intends. It will free up Iran’s path to a nuclear weapon...and it puts us at odds with our closest European allies."
President Rouhani: 'Iran will wait and see how others react'
President Hassan Rouhani has responded to the US withdrawal from the Iran nuclear agreement by saying the country is on standby to resume uranium enrichment, but that he will allow a few weeks for dialogue with the remaining parties first.
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The American-Israel Public Affairs Committee, a pro-Israel lobby group, called for bipartisan support to ensure Iran will never "acquire a nuclear weapons capability or realise its dangerous regional ambitions".
The lobby group described the original deal as "critically flawed", and said Trump's decision provides a new way to address the shortcomings of the deal after "the international community’s inability" to do so.
"We must once again use the tools of American diplomacy and economic pressure to fix the deal’s shortcomings and counter Iran’s malign activities."
Anthony Zurcher
BBC North America reporter
Image source, EPAShredding the Obama legacy
Since his inauguration, Mr Trump has taken aim at practically every one of his predecessor's signature achievements.
A pivot to Netanyahu
Trump's shift to a more vehemently anti-deal view tracks closely with his full-throated support of Benjamin Netanyahu and the hardline Israeli side of Middle East peace negotiations, after earlier suggesting he could be an impartial "deal-maker" in the region.
New faces in the room
Where once the president may have been counselled to be cautious in abandoning US commitments to Iran, this time his instincts - an innate distrust of multilateralism in general and Iran in particular - appear to have been enthusiastically supported.
After 15 months Mr Trump has built a foreign policy team that is largely on the same page - his page.
Image source, Getty ImagesYevgeny Serebrennikov, first deputy head of the defence and security committee in the Russian Upper House of Parliament, told the RIA news agency that Trump's decision puts the Korean peace process in doubt.
US Secretary of State Mike Pompeo is scheduled to arrive in North Korea soon to help further pave the way for forthcoming talks with the isolated regime.
Vladimir Chizhov, Russian envoy to the European Union, separately told RIA that Russia will continue efforts to keep the Iran nuclear deal functioning.
Image source, Getty ImagesObama visited Tokyo in March, where he met the Japanese Prime Minister
Former US President Barack Obama has just released a lengthy statement, calling Trump's decision "a serious mistake", and defending the agreement his administration helped negotiate.
"Without the JCPOA, the United States could eventually be left with a losing choice between a nuclear-armed Iran or another war in the Middle East," warns Obama.
He says the deal "is working", despite assessments by the current White House.
Obama calls it a "model for what diplomacy can accomplish - its inspections and verification regime is precisely what the United States should be working to put in place with North Korea".
"Indeed, at a time when we are all rooting for diplomacy with North Korea to succeed, walking away from the JCPOA risks losing a deal that accomplishes - with Iran - the very outcome that we are pursuing with the North Koreans."
Here's his full statement:
Image source, Getty ImagesIsraeli forces in the Golan Heights are on high alert after the US withdrawal announcement
Israeli forces in the Golan Heights remain on high alert after its military noted "irregular activity of Iranian forces in Syria".
Local authorities have been instructed to "unlock and ready [bomb] shelters," Reuters reports.
The initial announcement came moments before Trump's speech.
After Trump's address, Israeli Prime Minister Netanyahu said:
"For months now, Iran has been transferring lethal weaponry to its forces in Syria, with the purpose of striking at Israel... We will respond mightily to any attack on our territory."
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Paul Danahar
BBC Washington bureau chief
If they drank champagne in Saudi Arabia they would have been clinking glasses in Riyadh over President Trump’s decision to pull out of the nuclear deal with Tehran.
It means Saudi's biggest regional rival gets a financial kicking and Saudi Arabia gets to cash the cheque because the move is bound to spike oil prices.
The Israeli PM Benjamin Netanyahu also has reasons to celebrate. He was widely derided last week by EU diplomats for a presentation in which he claimed his agents had stolen new evidence showing Iranian duplicity.
It was old news on a new wrapper but Trump not only bought it, he cited it as proof he was right to leave the agreement.
Ironically the only other players in the Middle East who’ll be super happy with Trump’s move are those in Iran who chant: "Death to America."
The hardliners hated the deal and they’ll use its collapse to undermine the more moderate forces in the country who'd championed it.
Image source, Getty ImagesTrump and Saudi Arabia's Crown Prince Mohammed bin Salman in the Oval Office in March
Image source, ReutersUK Prime Minister Theresa May, German Chancellor Angela Merkel and French President Emmanuel Macron emphasised their "continuing commitment" to the deal in a joint statement.
"We encourage Iran to show restraint in response to the decision by the US; Iran must continue to meet its own obligations under the deal, co-operating fully and in a timely manner."
Image source, EPAEU High Representative/Vice President Federica Mogherini said in a statement as long as Iran remained committed, the EU would also continue "full and effective implementation" of the deal.
To Iran's citizens, Mogherini said: "Do not let anyone dismantle this agreement. It is one of the biggest achievements diplomacy has ever delivered."
European Council president Donald Tusk also weighed in on Twitter.
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Image source, Getty ImagesObama era Secretary of State John Kerry, who helped negotiate the original deal, issued a statement criticising Trump's decision.
He says it risks "dragging the world back to the brink we faced a few years ago".
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Yesterday, Trump slammed Kerry for engaging in "shadow diplomacy" in order to try to preserve the Iran nuclear deal.
Last month, Kerry met with Iranian Foreign Minister Javad Zarif at the United Nations in New York.
He also met German President Frank-Walter Steinmeier, French President Emmanuel Macron, and European Union foreign policy chief Federica Mogherini.
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Image source, Getty ImagesUN Secretary General Antonio Guterres is visiting Cuba today
UN Secretary General Antonio Guterres says he is deeply concerned by the US decision to withdraw from Iran nuclear deal, and calls on all other parties to fully abide by deal’s commitments.
"It is essential that all concerns regarding the implementation of the Plan be addressed through the mechanisms established in the JCPOA," he said.
Iran nuclear deal: Trump announces US withdrawal
The BBC's Rajini Vaidyanathan is at the US Congress speaking with lawmakers about what comes next.
Many have expressed concern about where this leaves the US from a national security perspective, and what consequence this decision will have on relationships with US allies.
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In a statement, Democratic Senator Dianne Feinstein said Trump's motivation for withdrawing was simple.
“Everything President Obama has done, this president wants to undo."
Image source, EPAHouse Speaker Paul Ryan called the Iran deal "deeply flawed" while expressing his support for Trump's decision
Top Republican Paul Ryan released a statement calling the Iran Deal "deeply flawed" and supporting Trump's decision.
"The president is right to insist that we hold Iran accountable both today and for the long-term. There will now be an implementation period for applying sanctions on Iran.
"During that time, it is my hope that the United States will continue to work with our allies to achieve consensus on addressing a range of destabilising Iranian behaviour - both nuclear and non-nuclear."
Iran's President Rouhani: "I have ordered Atomic Energy Organisation of Iran to be ready to start the enrichment of uranium at industrial levels. We will wait a few weeks and speak with our allies and those committed to JCPOA. All depends on our national interests."
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Image source, Getty ImagesDanon spoke to members of the security council after Trump's announcement
Israel's Ambassador to the UN Danny Danon said Trump's decision was "historic", providing "the prospect for a new era of security and stability in the Middle East".
Danon spoke to UN Security Council members following Trump's announcement.
“A united front against this regime that promotes terror and sows instability can put an end to the Iranian aggression which threatens our region and the entire international community.”
Image source, Getty ImagesBolton watched Trump alongside Vice-President Mike Pence
US National Security Adviser John Bolton tells reporters the US Treasury Department will allow up to 180 days for companies that do business with Iran to end their contracts or face sanctions.
Bolton, one of the architects of the US war on Iraq, was in the Diplomatic Reception Room with Trump as he made his announcement moments ago.
BBC White House reporter Tara McKelvey spoke to Bolton just now and says the normally unsmiling presidential adviser seemed in "good spirits".
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