Here are key reactions to Trump's biggest foreign policy move since taking office, turning his back on the deal known as the Joint Comprehensive Plan of Action (JCPOA):

- 'Psychological warfare' -

"This decision was an act of psychological warfare against Iran."

-- Iranian President Hassan Rouhani

- Uranium enrichment? -

"I have instructed the Iranian Atomic Energy Organization to take the necessary measures for future actions so that, if necessary, we can resume industrial enrichment without limit."

-- Rouhani

- Stay the course -

"Stay true to your commitments as we will stay true to ours and together with the rest of the international community, we will preserve this nuclear deal."

-- European Union diplomatic chief Federica Mogherini

- 'Regret' -

"France, Germany and the UK regret the US decision... The nuclear non-proliferation regime is at stake. We will work collectively on a broader framework, covering nuclear activity, the post-2025 period, ballistic activity and stability in the Middle East, notably Syria, Yemen and Iraq."

-- French President Emmanuel Macron, on Twitter

- Let it work -

"I urge the US to avoid taking any action that would hinder other parties from continuing to make the agreement work."

-- British Foreign Secretary Boris Johnson

- 'No confidence' -

"We hear that you want to continue the nuclear deal with the three European countries. I don't have confidence in these three countries. If you don't succeed in obtaining a definitive guarantee -- and I really doubt that you can -- at that moment, we cannot continue like this."

-- Iran's supreme leader Ayatollah Ali Khamenei in an address to the Iranian government

- 'US will lose' -

"Iran will never compromise on this agreement, and will abide by this agreement to the end... However, the US will lose in the end."

-- Turkish President Recep Tayyip Erdogan, according to a partial transcript of an interview released by CNN

- China defends deal -

"China will continue to uphold an impartial, objective and responsible attitude, remain in dialogue with all parties and continue to devote itself to safeguard and implement the deal."

-- Chinese foreign ministry spokesman Geng Shuang

- Moscow 'disappointed' -

Moscow is "deeply disappointed by the decision of US President Donald Trump to unilaterally refuse to carry out commitments under the Joint Comprehensive Plan of Action."

-- Russia's foreign ministry

- 'Instability' -

"The unilateral withdrawal of the United States from the nuclear deal is a decision that will cause instability and new conflicts."

-- Ibrahim Kalin, spokesman for President Recep Tayyip Erdogan, on Twitter

- Breaking commitment -

Damascus "strongly condemns the US president's decision to withdraw from the nuclear deal with Iran, which shows once again that the United States is not honouring its commitments and international agreements."

-- Syrian foreign ministry source quoted by the official SANA news agency.

- Compliance -

"I call on other JCPOA participants to abide fully by their respective commitments under the JCPOA and on all other member-states to support this agreement."

-- UN Secretary General Antonio Guterres

- 'Bold decision' -

"Israel fully supports President Trump's bold decision today to reject the disastrous nuclear deal with the terrorist regime in Tehran."

-- Israeli Prime Minister Benjamin Netanyahu

- Saudi support -

"The kingdom supports and welcomes the steps announced by the US president toward withdrawing from the nuclear deal... and reinstating economic sanctions against Iran."

-- Saudi Arabia's foreign ministry

- 'Misguided' -

"The reality is clear. The JCPOA is working... That is why today's announcement is so misguided... I believe that the decision to put the JCPOA at risk without any Iranian violation of the deal is a serious mistake."

-- former US president Barack Obama, whose administration brokered the 2015 deal

- Iran 'implementing ' deal -

"The IAEA can confirm that the nuclear-related commitments are being implemented by Iran."

-- The International Atomic Energy Agency in a statement