Iran nuclear deal: Why has Trump withdrawn US from it and why does it matter?

US President Donald Trump has fulfilled an election campaign promise to pull out of the landmark 2015 nuclear deal agreed between Iran and world powers, an agreement former Secretary of State John Kerry said “made the world a safer place”.

Mr Trump said the Obama-era legislation would be scrapped on Tuesday, calling the deal “decaying and rotten”.

The US will “not be held hostage to nuclear blackmail” or allow “a regime that chants “Death to America” to gain nuclear weapons, he said from the White House in a long-expected announcement.

The administration intends to reinstate severe sanctions against the Islamic Republic.

What is the Iran nuclear deal?

The Joint Comprehensive Plan of Action (JCPOA) was a two-year-long diplomatic initiative from Iran and a group of countries known as the P5+1 – the members of the United Nations Security Council (the US, UK, France, China, Russia) along with Germany.

The deal, reached in Vienna in July 2015 and later ratified by the UN, lifted crippling international sanctions in place on Iran in return for curbs on the country’s nuclear programme. It ensured that Tehran would abandon any attempts at creating a nuclear arsenal and ended 12 years of deadlock over the issue.

International Atomic Energy Agency (IAEA) monitors have consistently verified that Iran is complying with the terms of the deal.

Why has Trump withdrawn from it?

Mr Trump said that he believes the Iran nuclear agreement to be a bad deal long before he ran for office. Critics admit it is only a medium-term plan and it also does not address Iran’s non-nuclear weapons and missile programmes.

The president’s foreign policy has so far been marked by a significant ratcheting of tensions with Iran, driven by his administration’s noted friendliness towards Israel, which opposes the deal, and the appointment of Iran hawks to prominent positions in his administration.

The deal is also noted as former President Barack Obama’s greatest foreign policy achievement. In his first year in office Mr Trump has moved to dismantle several Obama-era laws and policies.

How did everyone else react?

In Iran, although President Hassan Rouhani called for restraint, some members of parliament burned American flags and chanted “Death to America”. Mr Rouhani says Iran remains committed to the deal.

UK Foreign Secretary Boris Johnson, as well as French President Emmanuel Macron, made trips to the US in the days leading up to the US’ certification deadline in a bid to save the deal, to no avail.

The EU issued a statement on Tuesday night rebuking Mr Trump’s decision, telling the US president he does not have the power to unilaterally scrap the international agreement.

By way of contrast, Israel – a key US ally which opposed the Iran deal – was delighted with the decision.

Prime Minister Benjamin Netanyahu praised his US counterpart for having the “courage” to withdraw from the deal.

“Israel has opposed the nuclear deal from the start because we said that rather than blocking Iran's path to a bomb, the deal actually paves Iran's path to an actual arsenal of nuclear bombs and this within a few years time,” he said.

So what happens next?

Mr Trump must decide which sanctions he wishes to re-impose on the Islamic Republic. Different baskets include penalties on Iran’s central bank, intended to hit Iranian oil exports, and more than 400 different companies, individuals and business sectors.

If the US were to scrap all the current waivers in one go, it would put the US in immediate violation of the deal’s terms, which say sanctions remain lifted as long as Iran is complying with its terms.

Iran is heavily invested in saving the deal, but has threatened that if sanctions are reinstated it could restart its nuclear programme.