Johnson "called for an end to hostilities" and said Britain viewed the 2015 nuclear deal as "the best arrangement currently available to deliver on our goal of stopping Iran from having a nuclear weapon", his spokesman said.

US President Donald Trump on Wednesday said "the time has come" for Britain, Germany, France, Russia and China to follow Washington's lead and abandon the 2015 nuclear agreement, which sets limits on Iran's enrichment levels.

Iran began breaking the deal's rules once Trump pulled the US out in 2018, resulting in a new wave of tension.

The US launched a drone attack in Iraq last week killing Iran's top military commander.

In a 20-minute call, Downing Street said Johnson wanted to "deliver the clear message" to Iran that "there is an urgent need for de-escalation".