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

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."

Late Sunday Iran announced a further rollback to its commitment to the troubled nuclear accord amid anger in the Islamic republic over the US killing top Iranian general Qasem Soleimani last week in a drone strike.

Rouhani told Johnson during the phone call that all the steps Iran has taken in reaction to the US' unilateral withdrawal from the nuclear deal in May 2018 are reversible, the Iranian president's office said in a statement.

Iran is willing to fully restore its nuclear commitments if the European parties to the agreement "go back to their (own) commitments" and help Tehran circumvent US sanctions, which were imposed by Washington in the wake of its withdrawal.

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 existing nuclear agreement, which sets limits on Iran's enrichment levels.

Rouhani insisted that Iran's strikes on Iraqi bases used by US troops in retaliation for Soleimani's killing were an act of "legitimate defence".

His office also said he asked Johnson to "reconsider" his position towards Soleimani, whose death the British prime minister said he did not regret.

"Without the efforts of the martyr Soleimani, you certainly would not be enjoying tranquility in London," Rouhani said, in reference to Soleimani's battle against the Islamic State group in both Iraq and Syria.