Britain's Foreign Secretary Boris Johnson is the latest international figure to urge US President Donald Trump to support the Iran nuclear deal.

Trump has made it clear he is no fan of the arrangement, which was negotiated in 2015 by his predecessor, Barack Obama, and which offers Iran eased economic sanctions in return for commitments that it will abandon its quest for nuclear weapons.

Trump has called the deal "insane" and has strongly hinted he will not sign an order due on May 12 that continues to suspend US sanctions. Should Trump not continue to support the nation's relaxation of sanctions, Iran might then resume its nuclear program.

AFP reported that Iran's President Hassan Rouhani has said the United States will face "historic regret" if it pulls out of the deal, which was signed in July 2015 by the US, China, Russia, Germany, France, Britain, Iran and representatives from the EU.

In a live speech on state television, Rouhani said: "Today all political factions, whether they be from the right, the left, the conservatives, reformers and moderates, are united."

China has called for the Iran nuclear deal to remain intact and be treated seriously. Foreign Ministry spokeswoman Hua Chunying said on April 27 that "China calls for all related parties to strengthen dialogue and coordination over the situation facing the Iran nuclear deal, to keep the deal intact and treat it seriously".

China will continue to safeguard and implement the deal in an objective, fair, and responsible manner, she said.

In recent weeks, several world leaders and senior diplomats－including German Chancellor Angela Merkel, French President Emmanuel Macron, and United Nations Secretary General Antonio Guterres－h(huán)ave attempted to persuade Trump not to walk away from the deal.

Open letter

While Johnson is not expected to meet Trump face-to-face while in the US, he has written an open letter published in The New York Times in which he says the deal, while imperfect, is better than the alternatives.

"At this delicate juncture," Johnson wrote. "It would be a mistake to walk away from the nuclear agreement and remove the restraints that it places on Iran."

He said inspectors from the International Atomic Energy Agency now have additional powers to monitor Iran's nuclear facilities, "increasing the likelihood that they would spot any attempt to build a weapon".

Johnson said ensuring Iran remained unable to develop a nuclear program was the best way to ensure it did not display "aggressive regional behavior".

And he noted that "only Iran would gain" from abandoning nuclear restrictions. The BBC reported that the UK's ambassador to the US, Kim Darroch, has also weighed in on the issue, telling US media: "We think that we can find some language, produce some action that meets the president's concerns."