A landmark nuclear deal between Iran and world powers is close to collapse, almost five years after it was agreed. Here's how it got to this point.
What did the deal do?
Iran has always insisted its nuclear programme is peaceful.
But suspicions it was being used as a cover to develop a nuclear bomb prompted the UN Security Council, US and EU to impose crippling sanctions from 2010.
In 2015, Iran reached a deal with six powers - the US, UK, France, China, Russia and Germany - that saw it limit its nuclear activities in return for sanctions relief.
The deal restricted Iran's enrichment of uranium, which is used to make reactor fuel but also nuclear weapons. It was also required to redesign a heavy-water reactor being built, whose spent fuel would contain plutonium suitable for a bomb, and allow international inspections.
Why is it close to collapse?
First, US President Donald Trump abandoned the deal in May 2018 and reinstated US sanctions. He wanted a new deal that would also curb Iran's ballistic missile programme and its involvement in regional conflicts.
Iran refused and saw the value of its currency plummet and its inflation rate soar as the sanctions took effect.
When the sanctions were tightened in May 2019, Iran took the first of five steps to "reduce" its commitments under the deal that related to uranium enrichment.
But it was in January 2020 that the accord moved towards total collapse.
Tensions escalated when a US drone strike in Iraq killed an Iranian general, Qasem Soleimani, and Iran responded with missile strikes Iraqi bases housing US troops.
Iran subsequently declared that it had suspended its final commitment on uranium enrichment. But it stressed that it was ready to reverse course if the US sanctions were lifted.
In response, France, Germany and the UK triggered the nuclear deal's formal dispute resolution mechanism - the first step towards reinstating international sanctions.
Iran warned the Europeans that if they abused the mechanism they would face "consequences".