British Prime Minister Boris Johnson and French President Emmanuel Macron reiterated their commitment on Sunday to the Iran nuclear deal and agreed a long-term framework was needed.

The leaders' statement follows European signatories to the nuclear deal triggering a diplomatic "dispute mechanism" last week - their strongest response yet to Tehran's steps away from the unravelling pact.

"On Iran, the leaders reiterated their commitment to the JCPOA [nuclear accord] and also acknowledged the need to define a long-term framework to prevent Iran acquiring a nuclear weapon," a Downing Street spokeswoman said in a statement after Johnson and Macron met on the sidelines of a Libya summit in Berlin.

"They agreed on the importance of de-escalation and of working with international partners to find a diplomatic way through the current tensions."

Following Washington's decision to withdraw from the historic agreement in May 2018, Iran began dropping its commitments under the deal.

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Josep Borrell, the European Union's foreign policy chief, said last week the aim of the dispute mechanism was not to reimpose sanctions, but "to find a solution for the return to full compliance" with the deal, which was also signed by Russia and China.

On January 6, days after the US assassination of a top Iranian general, Tehran took a further step by announcing it would scrap limits on enriching uranium, though it said it would continue cooperating with the United Nations nuclear watchdog.

The accord - deemed at the time to be a landmark achievement - sought to prevent Iran from developing nuclear weapons in exchange for sanctions relief and global powers beginning to welcome the country back into the international community.

But US President Donald Trump called it "the worst deal in history" and in May 2018 unilaterally withdrew from the deal, re-imposing crippling sanctions which have devastated Iran's economy. In response, Tehran challenged the European powers to fulfil their part of the deal and support its economy.

A new deal?

Johnson said last week he would be willing to work on a "Trump deal" to replace the international accord agreed between Iran, the five permanent members of the UN Security Council, plus Germany.

But his idea stands at odds with other European partners, which expressed "determination to work with all participants to preserve" the deal.

In an apparent bid to keep the door open for diplomacy, the three European signatories - known as the E3 - said they were not joining the US campaign to implement "maximum pressure" against Iran.

"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," they said.