Donald Trump has accused former Secretary of State John Kerry of “shadow diplomacy” for attempting to save the Iran nuclear deal, as the president prepares to announce whether he will pull out of the historic accord.

Mr Kerry, who helped negotiate the agreement under former President Barack Obama, has reportedly taken meetings with key architects of the deal in recent weeks, in an attempt to pressure the Trump administration into preserving it.

Mr Trump has made no secret of his disdain for the 2015 deal, repeatedly calling it the “worst deal ever made”. He lashed out at Mr Kerry over his attempts at “shadow diplomacy" on Monday, before announcing that he would make his final decision the next day.

“The United States does not need John Kerry’s possibly illegal Shadow Diplomacy on the very badly negotiated Iran Deal,” he wrote. “He was the one that created this MESS in the first place!”

Hours later, Mr Trump tweeted the he would announce his decision at 2 pm on Tuesday – days before his self-imposed deadline of 12 May.

Iran president Rouhani: US ending nuclear deal will be "historic regret"

Mr Kerry met with Iranian Foreign Minister Javad Zarif twice in two months to discuss ways of preserving the deal, according to the Boston Globe. He also talked separately with German President Frank-Walter Steinmeier, French President Emmanuel Macron, and European Union foreign policy chief Federica Mogherini, according to CNN.

He has also reportedly placed dozens of calls to members of Congress like Speaker of the House Paul Ryan.

A spokesman for Mr Kerry released a statement defending the former diplomat, saying that he thought all Americans would want "every voice possible urging Iran to remain in compliance with the nuclear agreement that prevented a war”.

“Secretary Kerry stays in touch with his former counterparts around the world just like every previous Secretary of State," spokesman Matthew Summers said. "Like America's closest allies, he believes it is important that the nuclear agreement, which took the world years to negotiate, remain effective as countries focus on stability in the region."

Iran's 'Trumpism' contest Show all 10 1 /10 Iran's 'Trumpism' contest Iran's 'Trumpism' contest A picture taken on July 3, 2017 shows a cartoon of US President Donald J. Trump and First Lady Melania Trump on display at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranian cartoonist Hadi Asadi poses for a picture with a trophy and an award next to cartoons of US President Donald J. Trump, at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranians look at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranian reformist cleric Mahmoud Doaei looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian man looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranian reformist cleric Mahmoud Doaei looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images

Mr Trump has repeatedly critiqued the deal for not going far enough on Iran's nuclear energy programme. He has also attacked the Obama administration for its role in the negotiations. At a recent National Rifle Association event, Mr Trump joked that Mr Kerry was “not the best negotiator we’ve ever seen”.

“He never walked away from the table except to be in that bicycle race where he fell and broke his leg,” he added, referencing an incident in which Mr Kerry fractured his femur while biking in the French Alps.

It is unclear where Mr Trump will land on the deal, in which six countries agreed to lift sanctions on Iran in exchange for limits on the country's nuclear energy production.

Diplomats familiar with the negotiations told the New York Times it was likely that Mr Trump would pull out of the deal and re-impose sanctions on Iran. Mr Macron signalled as much in a recent visit to the US, where he said the president would likely pull out for “domestic reasons”.

Mr Macron and German Chancellor Angela Merkel have both urged Mr Trump to stay in the deal. Iranian President Hassan Rouhani, meanwhile, has said the US will face “historic regret” if Mr Trump pulls out.