Hillary Clinton
Hillary ClintonReuters

Former U.S. Secretary of State and Democratic presidential candidate Hillary Clinton is warning that President Donald Trump's threat to pull out of the Iran nuclear accord is "dangerous", and suggesting he is undermining the validity of the United States' promises to other nations.

Clinton, in an interview recorded on Wednesday and set to air Sunday on CNN, spoke ahead of Trump's speech in which he confirmed he will not certify Iran's compliance with the 2015 nuclear deal.

The president's insistence on decertifying the deal, even though evidence has pointed to Iranian compliance, "makes us look foolish and small and plays right into Iranian hands", she said in the interview, which was quoted by The Associated Press.

"That is bad not just on the merits for this particular situation, but it sends a message across the globe that America's word is not good," she added.

"We have different presidents, and this particular president is, I think, upending the kind of trust and credibility of the United States' position and negotiation that is imperative to maintain," charged Clinton, who lost the presidential election to Trump.

Clinton, who as Secretary of State for President Barack Obama began negotiations on the deal, did acknowledge Iran is engaging in other dangerous behavior.

The 2016 Democratic presidential nominee also denounced Trump's language toward North Korea, charging that his verbal aggression has rattled American allies.

"We will now have an arms race — a nuclear arms race in East Asia," she warned, according to AP. "We will have the Japanese, who understandably are worried with missiles flying over them as the North Koreans have done, that they can't count on America."

She stressed that a diplomatic solution was preferred, suggested the inflammatory rhetoric played into North Korean leader Kim Jong Un's hands and bemoaned Trump's public undercutting of Secretary of State Rex Tillerson when he tweeted, "Save your energy, Rex", after Tillerson suggested negotiations.

"Diplomacy, preventing war, creating some deterrents is slow, hard-going, difficult work," said Clinton, adding, "And you can't have impulsive people or ideological people who basically say, 'Well, we're done with you.'"

Since losing the election to Trump, Clinton has continuously criticized her opponent. She recently warned that Trump “is a clear and present danger to America” and said she is "convinced" that his associates worked secretly with Russia to defeat her bid for presidency.

In her recently released book, “What Happened”, Clinton wrote that during the campaign Trump had invaded her personal space during a presidential debate.

Trump, who went on to win the election and become President of the United States, stood behind Clinton during the second presidential debate in St. Louis on October 9, 2016.

"No matter where I walked, he followed me closely, staring at me, making faces," Clinton wrote. "It was incredibly uncomfortable."

"My skin crawled," she added.