Britain, France and Germany made a last-ditch appeal Monday to US President Donald Trump not to abandon the Iran nuclear deal as a key deadline approaches, warning that scrapping it would spark an "escalation".
Trump has threatened to withdraw from the 2015 pact when it comes up for renewal on May 12, and to reimpose sanctions unless European signatory states fix its "terrible flaws".
German Foreign Minister Heiko Maas warned that the accord's collapse could spark "an escalation" in the region and stressed that Washington's key European allies remain convinced saving it "makes the world a safer place".
His French counterpart Jean-Yves Le Drian, on a Berlin visit, said that the agreement is "the right way to stop Iran from getting access to nuclear weapons" and "will save us from nuclear proliferation".
British Foreign Secretary Boris Johnson, who was visiting Washington Monday, cautioned that "at this delicate juncture, it would be a mistake to walk away from the nuclear agreement and remove the restraints that it places on Iran".
"Now that these handcuffs are in place, I see no possible advantage in casting them aside," Johnson wrote in The New York Times.
He argued that "every available alternative is worse", adding that "the wisest course would be to improve the handcuffs rather than break them".
Under the landmark nuclear pact, also signed by Russia and China, Iran pledged not to build a nuclear bomb in return for relief from international sanctions.
Trump has consistently complained about the agreement, reached under his predecessor Barack Obama, citing perceived flaws including "sunset" provisions lifting some nuclear restrictions from 2025.
In an attempt to salvage the deal, French President Emmanuel Macron has pushed to extend its scope to address this issue, as well as Iran's missile capabilities and its role in the region.
Israel has also pushed to have the accord ditched, arguing that intelligence documents it recently unveiled showed that Iran had had a secret atomic weapons programme which it could re-activate at any time.
Britain, France and other signatories have said those arguments only strengthened the case for the deal, which has safeguards in place designed to keep Iran from pursuing atomic weapons.
Johnson was Monday to start a two-day visit to Washington, with the nuclear deal top of the agenda, the Foreign Office said.
He was due to meet US Vice President Mike Pence, National Security Advisor John Bolton and Congressional foreign policy leaders.
He said in his article that Britain, the US and Europe were "united in our effort to tackle the kind of Iranian behaviour that makes the Middle East region less secure -– its cyber activities, its support for groups like Hezbollah, and its dangerous missile programme".
Iran's support for Syrian President Bashar al-Assad, via the Lebanese armed group Hezbollah in Syria's civil war, and its backing for Shiite Huthi rebels in Yemen have added to frictions between Tehran and Western powers.
Iran has always denied it sought a nuclear weapon, insisting its atomic programme was for civilian purposes.
Its President Hassan Rouhani on Sunday issued a strong warning to the United States not the quit the pact.
"If the United States leaves the nuclear agreement, you will soon see that they will regret it like never before in history," the reform-minded Rouhani said in a televised speech.
"Trump must know that our people are united, the Zionist regime (Israel) must know that our people are united," he said.
He also vehemently reiterated his country's opposition to curtailing its non-nuclear missile capabilities.
Tehran "will build as many missiles and weapons as needed" for its defence, he said.
"We are honouring our commitment, but we are telling the whole world we will not negotiate with anyone about our weapons and our defence."