The Iran nuclear agreement, formally known as the Joint Comprehensive Plan of Action, is a landmark accord reached between Iran and world powers including the US in July 2015.
Under the agreement, Iran agreed not to produce either the highly enriched uranium or the plutonium that could be used in a nuclear weapon in exchange for international sanctions relief, with extensive international inspections monitoring activity.
Before the JCPOA, Iran negotiated for years with western countries to offer incentives to halt its nuclear enrichment.
Iran has in the past denied seeking nuclear weapons, saying it refines uranium for civilian energy uses only.
The nuclear deal capped the purity to which Tehran can refine uranium at 3.67 per cent, the level suitable for most civilian nuclear energy, well below the 20 per cent achieved before the 2015 deal and the 90 per cent suitable for a nuclear weapon.
Here are the highs and lows of the JCPOA in the last seven years:
In May 2015, Barack Obama as president signed the agreement into US law. The Senate passed the legislation by a 98-1 vote and the House by a 400-25 vote.
The deal was agreed with a group of world powers known as the P5+1 — the US, UK, France, China, Russia and Germany.
The JCPOA is part of UN Security Council Resolution 2231. The members of the UN Security Council voted on it on July 20, 2015, and adopted it on October 18.
It came into effect on January 16, 2016. In the same month, International sanctions on Iran were lifted.
International nuclear watchdog, the IAEA, said its inspectors had verified that Iran had taken the required steps.
In May 2018, president Donald Trump withdrew the US from the deal. He described it as “defective at its core”.
Iran resumed some of its nuclear activities in response.
Mr Trump reinstated all US sanctions on Iran that November as part of a “maximum pressure” campaign against Tehran.
A year after withdrawing the US from the deal, Mr Trump imposed new sanctions on Iran, this time aimed at its industrial metals sector.
The move came after Tehran said that it would no longer fully comply with the JCPOA.
Iran accused the other parties in the deal of not making good on their promises to shield its oil and banking sectors from US sanctions.
Talks to revive the JCPOA began five months after Joe Biden succeeded Mr Trump as president in January 2021.
Mr Biden said the US would rejoin the deal and lift the sanctions if Iran reversed its breaches.
Ebrahim Raisi, who took up office as Iranian president in August, said the US must make the first move and insisted that Washington should lift sanctions first.
By November 2021, Iran had amassed a stockpile of enriched uranium that was many times larger than permitted.
The UN nuclear watchdog said Tehran had begun the process of enriching uranium to 60 per cent fissile purity at an above-ground nuclear plant at Natanz.
On February 4 the US State Department said it would waive sanctions on Iran’s civil nuclear programme.
It represented a technical step necessary to return to the 2015 agreement.
The US decision came as US negotiators returned to Vienna for negotiations.
Iran says that Russia's demand for written US guarantees that sanctions on Moscow would not harm Russian co-operation with Iran is “not constructive” for talks with global powers.
The announcement by Russia, which could wreck months of indirect talks between Tehran and Washington in Vienna, came shortly after Tehran said it had agreed a road map with the UN nuclear watchdog to resolve outstanding issues that could help secure the nuclear pact.