Washington: Donald Trump and his main challenger for the Republican presidential nomination, Ted Cruz, have escalated their bitter feud, taking to social media to clash over two unlikely figures: their wives.

An anti-Trump political group unveiled a controversial campaign ad ahead of Tuesday’s votes in Arizona and Utah that uses a photograph of Trump’s wife Melania lying provocatively in his custom-fitted jet, naked and handcuffed to a briefcase.

‘Meet Melania Trump, your next first lady,’ read the online ad, posted on Facebook by the group Make America Awesome.

‘Or, you could support Ted Cruz on Tuesday.’

Melania Trump, 45, is a Slovenian-American jewelry designer and former model.

The use of the image, from a GQ magazine photo shoot in 2000 when she was Melania Knauss and not yet married to Trump, angered the billionaire real estate magnate, who made his own veiled threat about Cruz’s wife Heidi in a tweet late Tuesday.

‘Lyin’ Ted Cruz just used a picture of Melania from a GQ shoot in his ad. Be careful, Lyin’ Ted, or I will spill the beans on your wife!’ Trump posted to his seven million Twitter followers.

Cruz wasted no time firing back.

‘Pic of your wife not from us,’ Cruz tweeted. ‘Donald, if you try to attack Heidi, you’re more of a coward than I thought. #classless.’

Trump Thursday retweeted a seemingly unflattering photo of Cruz’s wife, Heidi.

Cruz told reporters in Wisconsin, pointing his fingers angrily at TV cameras: ‘It’s not easy to tick me off. I don’t get angry often. But you mess with my wife, you mess with my kids, that’ll do it every time. Donald you are a sniveling coward and leave Heidi the hell alone.’

The suggestive ad featuring Trump’s wife was apparently part of an effort to sway voters in predominantly Mormon Utah by appealing to the morality of the state’s socially conservative population, according to The New York Times.

Cruz comfortably won Utah and Trump finished third behind Ohio Governor John Kasich. Trump easily won Arizona in the day’s other Republican contest.

Heidi Cruz, 43, is an investment manager who has taken a leave of absence from her position at Goldman Sachs to hit the campaign trail with her husband.

She swatted away Trump’s threat, saying she was ‘not worried’ about his bluster.

‘You probably know that most of the things that Donald Trump says has no basis in reality,’ she told reporters in Wisconsin, which votes 5 April.

‘We have run our campaign with the principles that Ted and I believe in and a lot of the things that are done from time to time are not from our campaign.’