DONALD Trump described the Iran nuclear deal as the "worst ever" agreement negotiated by the US.
The US President claimed Iran was still developing its nuke programme. Here's what you need to know.
Why has Donald Trump pulled out of the Iran nuclear deal?
Announcing his decision to withdraw in July 2018 to announce his decision, he said: “The so-called Iran deal was supposed to protect the United States and our allies from the lunacy of an Iranian nuclear bomb, a weapon that will only endanger the survival of the Iranian regime.
“In fact, the deal allowed Iran to continue enriching uranium and over time reach the brink of a nuclear blackout.”
“Today, we have definitive proof that this Iranian promise was a lie."
The Republican, who called the agreement "rotting and decaying", said he would impose the "highest level" of economic sanctions on Iran.
He said: "The United States no longer makes empty threats. When I make promises, I keep them."
What sanctions are the US reinstating?
Washington will reintroduce far-reaching sanctions on Iran's vital oil sales and banking sectors on Monday November 5 2018.
This will try to force the Islamic Republic into negotiations to scrap its nuclear energy and ballistic missile programmes and end its support for proxies in conflicts across the Middle East.
The Trump administration said that eight importing countries would temporarily be allowed to keep buying Iranian oil when sanctions come back into effect.
Iran is the world's No. 3 oil exporter.
Ayatollah Ali Khamenei also said Iran's arch-adversary the United States had failed to reassert its domination over Iran since the country's 1979 Islamic Revolution that toppled the U.S.-backed Shah.
He said: "The world opposes every decision made by Trump."
The US has now threatened to impose the "strongest sanctions in history" against Iran.
Secretary of State Mike Pompeo laid out 12 demands for Iran and said relief from economic sanctions would only come when Washington had seen tangible shifts in Iran's policies.
He warned: "The sting of sanctions will be painful if the regime does not change its course from the unacceptable and unproductive path it has chosen to one that rejoins the league of nations."
Pompeo said a stronger pact should require that Iran stop enrichment of uranium, which was allowed within strict limitations under the previous deal.
Iran would also have to walk away from core pillars of its foreign policy, including its involvement in Syria, Yemen, Lebanon and Afghanistan.
How has Iran responded?
A year after Trump announced he wants the US to withdraw from the nuclear deal, Iran's leader said it wants to reduce its "commitments".
On May 8, 2019, Iran's President Hassan Rouhani said in a televised speech the country would reduce its "commitments" to the deal, but not fully withdraw.
He claimed the US had "spared no effort" in trying to undermine the deal.
Rouhani said he would now keep enriched uranium stocks in the country rather than sell them abroad and also threatened to resume production of higher enriched uranium in 60 days.
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What is the Iran nuclear deal?
The deal was an agreement between the Islamic Republic and a group of world powers aimed at scrapping the Middle Eastern country's nuclear weapons programme.
It saw Iran agree to eliminate its stockpile of medium-enriched uranium by 98 per cent.
According to the deal, Iran would receive relief from the US, European Union, and the United Nations Security Council on all nuclear-related economic sanctions.
The agreement was reached on July 14, 2015, and the world powers signed it in Vienna.
However, on May 8, 2018, President Trump announced the US will withdraw from the agreement - which he has repeatedly called "insane" and ridiculous".
America's withdrawal from the agreement mean crippling economic sanctions will once again be placed on Iran - further heightening tensions between the two countries.
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