US President Donald Trump is facing mounting pressure from international bodies and personalities and Washington's European allies to stick with the 2015 nuclear agreement.
The deal with the six major powers curtailed Tehran's nuclear program in return for relief from international sanctions.
Trump appears poised to announce in the coming days that he will no longer certify that Iran is upholding its side of the deal.
Trump's antagonism to the accord, dates back to the lead-up to the 2016 US presidential election, where he branded it "the worst deal ever".
Former British foreign minister William Hague believes Trump is desperate to stand by his campaign rhetoric despite the repeated reports by the UN nuclear watchdog that Tehran has adhered to its commitments under the deal.
"He wants to be able to live up to his rhetoric and say they are not keeping the agreement, but the awkward truth for him is that they are faithfully sticking to it, as certified by the IAEA," Hague wrote in an op-ed published in the Daily Telegraph on Tuesday.
He denounced Trump's harsh line on the landmark accord, acknowledging it as "the best deal".
"As someone who was involved in its negotiation in the early stages, I can testify that it was also the best deal available in the circumstances."
Hague said Trump's likely decertification is apparently intended to ultimately get the US Congress to delay resuming the application of the suspended sanctions, but essentially passing future decisions on that over to the legislature.
***So Mistaken
Such a decision would be "so mistaken", the ex-diplomat said.
"The trouble is that this could easily lead to the unraveling of the whole deal, which will clearly lack the support of the president and will be at the mercy of members of Congress running for election and each trying to show they are tough on Iran," he said.
"The main reason such a decision would be so mistaken, even if there are no immediate consequences, is that it will reinforce the idea that the word of America cannot be trusted; an agreement solemnly entered into by one president can be steadily eroded by the next one. The effects of that will be long term and profound."
He warned that such a move could alienate Washington's key allies, dissuading them from engaging with the US on any future international issue of fundamental importance.
"It will be cheered on only by Israel, and perhaps Saudi Arabia and the UAE, [which] have never been happy with the agreement but were also getting desperately worried when there wasn't one," the ex-British diplomat said.
His view was echoed in a New York Times article by Wendy Sherman, the US undersecretary of state for political affairs and the lead nuclear negotiator under Trump's predecessor Barack Obama.
***Grave Consequences
Sherman had warned that the consequences of Trump's anti-deal attempts would be grave for the United States.
"If President Trump undermines the nuclear deal, the repercussions for American foreign policy will be disastrous: It will drive a wedge between the United States and Europe, weakening the critical trans-Atlantic relationship and increasing the influence of Iran, Russia and China," she said.
"Whether the Trump administration's decertification unravels the deal quickly or slowly, unjustified unilateral American action will give the Iranians the moral high ground, allowing them to rightly say that it was the United States, not them, who killed the deal."
Sherman wrote that if Iran stays in the agreement with the other countries who are party to it, the United States will lose any standing to bring concerns to the Joint Commission, the forum the agreement set up to oversee progress; any evidence we might offer about suspect Iranian military sites will be viewed with suspicion.
***Affront to UN
A former Swedish diplomat criticized a possible US withdrawal as a new affront to the United Nations.
"If Mr. Trump cares for the authority of the United Nations, then he cannot pull back unilaterally from that agreement," former UN weapons inspector, Hans Blix, warned.
"I am a bit puzzled by Trump's lonely attitude ... because the president has voiced his great disapproval" of the Iran deal in the face of "almost the unanimous international community standing in favor of it", he was quoted as saying by France 24.
Adding to the pressure on the beleaguered US leader, the nuclear weapons disarmament campaign group that last week won the 2017 Nobel Peace Prize urged him to uphold the deal to "avoid causing any more conflict".
"We really call on the US government to continue to certify and stay in this deal," Beatrice Fihn, director of the International Campaign to Abolish Nuclear Weapons told a news conference at the UN headquarters in New York.
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