Cover Image: PA
Donald Trump will announce whether he will pull the United States out of the Iran nuclear deal on Tuesday evening (7pm BST).
The agreement - struck in 2015 - saw Tehran agree to get rid of its weapons programme, if crippling sanctions were lifted.
Mr Trump branded the deal - agreed by his predecessor Barack Obama - as the "worst" ever backed by the US.
The Foreign Secretary Boris Johnson suggested that if the US withdraws, then Iran would "go for a bomb".
Former Conservative leader William Hague has urged US president Donald Trump not to withdraw from the Iran nuclear deal - saying it would "broadcast a message that Washington does not honour its word".
Mr Hague, writing in the Daily Telegraph, said that ripping up the deal would be a "very great error".
He wrote: "If he is wavering, he should picture himself sitting across from Kim (Jong-Un) in the near future."
He said Mr Kim is less interested in Mr Trump keeping his word than whether the United States does.
"Ending the Iran deal would mean that what the US signs up to in one year, it can abrogate three years later.
"And that, in turn, would not bode well for an agreement with North Korea or the stability of the Middle East - and thereby for the peace of the world."
Foreign Secretary Boris Johnson's visit to Washington has shown up Britain's lack of influence with the US administration, shadow foreign secretary Emily Thornberry has said.
Ms Thornberry said that while France's President Emmanuel Macron and German Chancellor Angela Merkel had held face-to-face talks with Donald Trump, Mr Johnson's intervention was restricted to an appearance on Fox News.
"I think that is a by-product of a long and unnecessary indulgence of Donald Trump that has been happening for too long by this Government," she told the BBC Radio 4 Today programme.
"I think that if you allow the new president to believe that that sort of behaviour is normal then I think that your influence later is less."