Signed in the year 2015, between Iran and P5+1 countries (China, Russia, France, United States, Germany and the UK) in Vienna, the accord, orchestrated by the Obama administration, called for Iran to accept restraints on its nuclear programme in return for the lifting of UN, European and US nuclear-related economic sanctions.
The tension between Iran and spiked after Trump pulled out from the deal in May last year alleging that Iran hadn't done enough to limit its weapons stockpile and had continued to work on its nuclear programme. Iran has denied any such allegations.
Since then, Tehran has gradually taken steps to reduce its compliance with the deal, which prompted Britain, France and Germany to formally accuse it on Tuesday of violating the terms.
The tension between both countries reached new low earlier this month after the US killed an Iranian general in a drone strike in Baghdad.
Tehran responded a week ago by launching missiles at US targets in Iraq.