FORMER US president Barack Obama made a rare public criticism of his successor early this morning, describing US President Donald Trump’s decision to abandon the Iran nuclear deal as “misguided” and a “serious mistake.”

“The reality is clear. The JCPOA is working,” Mr Obama said in a statement, referring to the deal his administration brokered in 2015. “That is a view shared by our European allies, independent experts, and the current US secretary of defence.”

“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,” he said.

“The consistent flouting of agreements that our country is a party to risks eroding America’s credibility, and puts us at odds with the world’s major powers.”

Mr Obama said that without the deal, the US “could eventually be left with a losing choice between a nuclear-armed Iran or another war in the Middle East.”

He said the deal remains a model for what diplomacy can accomplish, including when it comes to North Korea.

Austrlaia’s Prime Minister Malcolm Turnbull is urging all parties to the Iran nuclear deal to show restraint in their response to Trump’s decision to withdraw the US from the agreement.

After months of threatening he would abandon what he labelled “the worst deal ever made”, the president confirmed his position early on Wednesday.

“I wouldn’t foreshadow a complete unravelling of the deal,” Mr Turnbull told ABC Radio as he noted Iran and European signatories were showing initial restraint.

Mr Obama’s criticism came amid Mr Trump’s decision to withdraw the US from the Iran nuclear deal.

Mr Trump said that the Iran nuclear agreement, called the Joint Comprehensive Plan of Action (JCPOA), was a “horrible, one-sided deal” that “didn’t bring peace” and “never will”.

He described the deal as “defective at its core”.

The 2015 deal, worked out by the United States, five other international powers and Iran, eased sanctions on Iran in exchange for Tehran limiting its nuclear program.

Mr Trump said the agreement does not address Iran’s ballistic missile program, its nuclear activities beyond 2025 nor its role in conflicts in Yemen and Syria.

After making the announcement, Mr Trump signed a presidential memorandum to reinstate the “highest level of economic sanctions” against Iran.

He said if he allowed the deal to stand, there would soon be a nuclear arms race.

Mr Trump called Iran a “regime of great terror” and that “no action taken by the regime has been more dangerous than its pursuit of nuclear weapons and the means of delivering them.”

Mr Trump said the US had “definite proof” that Iran was lying about its pursuit of nuclear weapons when it entered into the 2015 agreement.

He said any nation that was found assisting Iran to acquire nuclear weapons would also face sanctions.

“If the regime continues its nuclear aspirations, it will have bigger problems than it has ever had before,” he said. “It is clear to me that we cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement.”

Security Advisor John Bolton said that European firms would have a “wind down” period to cancel any investments made in Iran under the terms of the accord

Mr Trump said he understood why Iran has said it won’t return to the negotiating table.

“That’s fine. I’d probably say the same thing if I were in their position,” Mr Trump said. “But the fact is they are probably going to want to make a new and lasting deal. ... When they do I am ready willing and able.”

Iran’s President Hassan Rouhani said his country would remain in the JCPOA with the other signatories.

Mr Rouhani was reportedly furious at the announcement, accusing Mr Trump of “psychological warfare” and vowing to take the matter up with the agreement’s other signatories, including Washington’s rivals in Moscow and Beijing.

Israeli Prime Minister Benjamin Netanyahu called Mr Trump’s decision “brave and correct”.

However, French President Emmanuel Macron said that France, Britain and Germany regret Mr Trump’s decision to quit the agreement.

“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,” he said.

European Union president Donald Tusk said Mr Trump’s decision “will meet a united European approach.”

The European Union’s chief diplomat Federica Mogherini, who helped oversee the talks with Iran that led to the JCPOA, insisted the accord “is delivering on its goal which is guaranteeing that Iran doesn’t develop nuclear weapons.”

“The European Union is determined to preserve it,” she said.

WHAT HAPPENS NOW?
The 2015 deal, signed by the US, Britain, France, Germany, Russia, China, and Iran, lifted years of economic sanctions against Iran.

Sanctions imposed on Iran in early 2012 by the US and European Union over its nuclear program cut Iran’s crude exports from a peak of 2.5 million barrels per day before the sanctions to a little more than one million barrels.

In exchange for those sanctions being lifted, Iran, which was on the brink of being about to produce fuel for nuclear bombs, agreed to strict limits on its nuclear program.

Under US law, the president has to certify to Congress that Iran is complying with the deal every 90 days.

Iranian president Hassan Rouhani said before Mr Trump’s decision he wants the deal to continue without the US involved.

“We are not worried about America’s cruel decisions … We are prepared for all scenarios and no change will occur in our lives next week,” he said in a speech broadcast on state TV.

“If we can get what we want from a deal without America, then Iran will continue to remain committed to the deal. What Iran wants is our interests to be guaranteed by its non-American signatories … In that case, getting rid of America’s mischievous presence will be fine for Iran.”

Iran has said that it will not renegotiate a deal that took two-and-a-half years to get signed off.

Given Iran is a major exporter of oil, Mr Trump’s decision could disrupt the global oil supply.

Both French President Emmanuel Macron and German leader Angela Merkel have made repeated personal pleas to Mr Trump in face-to-face meetings in Washington during the past fortnight.

Former Obama administration officials warned that the decision puts the US on a collision course with Iran, distances the White House from its key allies and put US citizens held in Iran at risk.

Former deputy secretary of state Tony Blinken, who helped negotiate the accord, called it a “monumental mistake” and former senior diplomat Wendy Sherman told reporters Trump was putting international stability at risk for purely domestic political purposes.

“This has been a crisis that Trump has been precipitating himself to answer his base, to fulfil a campaign pledge that he made, without any sense whatsoever of what Plan B is,” she told reporters.

“It says that the United States is not a reliable partner,” she added, insisting that the existing deal permanently prevents Iran from gaining a nuclear weapon.