Three EU countries on Tuesday said they were launching a dispute mechanism against Iran under the 2015 nuclear deal, accusing Tehran of repeatedly violating the accord while insisting they remained committed to the agreement.

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 foreign ministers of the three European nations 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, their statement said, adding Tehran was not "meeting its commitments".

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 which could reimpose sanctions.

Iran had intensified sensitive activities to enrich uranium -- which can be used to make a nuclear weapon -- in response to the United States pulling out of the deal in 2018.

Its latest step in January to forego the limit on the number of centrifuges used in uranium enrichment prompted the Europeans to trigger the mechanism.

"Iran's actions are inconsistent with the provisions of the nuclear agreement and have increasingly severe and non-reversible proliferation implications," the statement said.

'Back to full compliance'

But the three powers said they "once again express our commitment" to the deal 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 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 Iran has not benefitted from the sanctions relief it had hoped for, creating more trouble for its already battered economy. The country also saw highly unusual protests in November sparked by a surprise petrol price rise.

Yet even as the EU powers made clear their committment to the deal, British Prime Minister Boris Johnson said Tuesday he would be willing to work on a "Trump deal" to replace the JCPoA.

"If we are going to get rid of it, let's replace it and let's replace it with the Trump deal," he said.

"That's what we need to see. I think that would be a great way forward," he added, noting that "from the American perspective it's a flawed agreement."

'Resume diplomatic effort'

But EU's diplomatic chief Josep Borrell said it was "more important than ever" to save the 2015 Iranian nuclear deal "in light of the ongoing dangerous escalations in the Middle East."

Tensions between Iran and the United States last week climbed to their highest levels since the hostage crisis at the Tehran US embassy that followed the 1979 Islamic Revolution which ousted the pro-American shah.

The United States killed Soleimani in a strike in the Iraqi capital Baghdad, prompting vows of retribution by Iran.

And while Iran's attack on Iraqi bases housing US troops was seen as a relatively measured retaliation, Iranian forces mistakenly shot down over a Tehran a Ukrainian plane killing all 176 passengers and crew on board.

Analysts have said the Europeans still have an opportunity to press for diplomacy, with Tehran on the defensive after admitting shooting down the airliner.

"I see an opportunity to re-engage at least on the nuclear front," Alex Vatanka, senior fellow at the Washington-based Middle East Institute told AFP. "I think the Iranians would do it, in a multilateral setting."