The move by Britain, France and Germany comes as tensions soar between the West and Iran following the killing of top commander Qasem Soleimani in a US strike and the admission by Tehran days later it had accidentally shot down a Ukrainian airliner.

The 2015 nuclear deal -- known as The Joint Comprehensive Plan of Action (JCPoA) -- has a provision that allows a party to claim significant non-compliance by another party before a joint commission.

If the issue is not resolved at the joint commission, it then goes to an advisory board and eventually to the UN Security Council.

The foreign ministers of Britain, France and Germany said Iran had been progressively scaling back its commitments under the deal and defying key restrictions on its nuclear programme since May last year.

"We have therefore been left with no choice, given Iran's actions" to begin the dispute process, Tuesday's statement said, adding Tehran was not "meeting its commitments".

But the three powers said they "once again express our commitment" to the deal -- which the United States withdrew from in 2018 -- and expressed "determination to work with all participants to preserve it".

"Given recent events, it is all the more important that we do not add a nuclear proliferation crisis to the current escalation threatening the whole region," the statement added.

"Our hope is to bring Iran back into full compliance with its commitments under the JCPoA."

The accord aimed to restrict Iran's nuclear ambitions -- which Western powers feared were aimed at developing atomic weapons -- in return for sanctions relief.

The three countries said they would not join "a campaign to implement maximum pressure against Iran" championed by US President Donald Trump.

Trump's move meant that Iran has not benefitted from the sanctions relief it had hoped for, creating more trouble for its already battered economy.