He has long threatened to withdraw from the agreement, signed during Barack Obama’s presidency, and has called it the “worst ever deal negotiated” because it does not address Iran’s ballistic missile programme or its role in the wars in Syria And Yemen, nor permanently block Tehran from developing atomic weapon.

European leaders have warned that a US withdrawal would undo years of work that led to and sustained a landmark deal that has kept nuclear weapons out of Iran’s hands.

On Tuesday morning France’s defense minister said weakening the agreement would aggravate tensions in the Middle East.

Boris Johnson also visited Washington on Monday, conducting talks with Vice President Mike Pence and the new secretary of state Mike Pompeo.

A senior US official who is close to the decision-making process said France, Germany and the UK had shifted significantly to address Mr Trump’s concerns about ballistic missiles, the terms governing international inspectors’ visits to Iranian sites, and “sunset” clauses under which some terms of the deal expire.

In the past few weeks, Mr Trump has consulted either in person or by telephone with leaders of all three countries.

And Iran has said it will not renegotiate, threatening to retaliate if Mr Trump pulls the US out and re-imposes sanctions, but has not said how.

Diplomats and military experts said Tehran could seek to resume its nuclear arms programme or step up its military involvement in Iraq, Syria, Yemen and Lebanon.

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