Donald Trump has announced his administration will refuse to re-certify the Iran nuclear deal, citing "multiple violations" and saying Iran had not lived up to the "spirit" of the deal. The US government also slapped further sanction on Iran's Revolutionary Guard.
The president has been highly critical of the agreement which curbs Iran's abilities to produce nuclear weapons, and had promised during his election campaign to scrap it all together.
Trump has often described it as a "bad deal" and an "embarrassment" to the US. On Wednesday 11 October, he told Fox News, "I think it was one of the most incompetently drawn deals I've ever seen."
He has been urged by world leaders and officials to maintain the accord and stick by the deal.
Theresa May told the president in a phone call that the deal was "vitally important for regional security".
And the EU's external affairs secretary Helga Schmid said the the deal "was a major political achievement and an excellent example of successful multilateral diplomacy. It demonstrated what can be achieved through cooperation rather than confrontation."
Should Trump decertify the deal, it would create a 60-day window for Congress to impose fresh sanctions on Iran. Any new sanctions would remove the US from the deal.
Ahead of Trump's announcement, the White House said that "the full range of the Iranian regime's malign activities extends well beyond the nuclear threat it poses."
European allies who have praised the agreement are unlikely to reimpose their own sanctions but this will depend on what reaction the US departure would receive from Tehran.
What is the Iran nuclear deal?
Officially known as the 2015 Joint Comprehensive Plan of Action, it was designed to prevent Iran from being able to produce nuclear weapons.
Sanctions that had crippled the country for years were eased and in return, Iran restricted its involvement with nuclear development.
This included reducing the work associated with the enrichment of uranium, allowing regular inspections from outside monitors as well as the ban on new heavy-water reactors for 15 years.
Under the agreement, the US must recertify the deal every 90 days to ensure that Iran is biding by the rules.
Donald Trump has resigned the agreement twice, but has been heavily critical of the plan.