UN Ambassador Nikki Haley called a tawdry rumour fuelled by a damning White House exposé that she was having an affair with US President Donald Trump “disgusting” and “highly offensive”.

The 46-year-old Haley, married for 22 years and the mother of two children, lashed out in an interview with Politico at the suggestion made by Fire and Fury author Michael Wolff that he was “absolutely sure” that Mr Trump, 71, was having an affair.

The New York Post reports that Wolff said readers of his book would find a clue about who the president’s supposed paramour was in his book, which paints an unflattering picture of Mr Trump’s White House but has also been panned by critics for its inaccuracies.

“Now that I’ve told you, when you hit that paragraph, you’re gonna say, ‘Bingo,’” he said on Real Time with Bill Maher last week.

People soon singled out a paragraph that mentioned Ms Haley and the rumour mill caught fire.

“The president had been spending a notable amount of private time with Haley on air force One and was seen to be grooming her for a national political future,” the passage read.

“It is absolutely not true,” Ms Haley told the website, arguing that she had little direct contact with the commander-in-chief, who has been accused of sexual misconduct or assault by more than a dozen women — and who was recently linked to porn vixen Stormy Daniels.

The thrice-married Mr Trump and administration spokeswoman Sarah Huckabee Sanders have repeatedly called all the women liars and denied any impropriety.

“I have literally been on air force One once and there were several people in the room when I was there,” Ms Haley said.

“[Wolff] says that I’ve been talking a lot with the president in the Oval about my political future. I’ve never talked once to the president about my future and I am never alone with him. So the idea that these things come out, that’s a problem,” she said, adding that such allegations are commonly lodged against powerful women.

“But it goes to a bigger issue that we need to always be conscious of: At every point in my life, I’ve noticed that if you speak your mind and you’re strong about it and you say what you believe, there is a small percentage of people that resent that and the way they deal with it is to try and throw arrows, lies or not,” she declared.

The former South Carolina governor said during the campaign that she was “not a fan” of Mr Trump, who had attacked her on Twitter.

“The people of South Carolina are embarrassed by Nikki Haley!” Mr Trump tweeted at the time.