Ted Cruz has accused Republican presidential rival Donald Trump of stoking false rumours about his personal life, claiming the billionaire businessman is trafficking in "sleaze" and "slime".
Speaking to reporters in Wisconsin, Mr Cruz said the campaign has taken a "darker turn". He accused Mr Trump and "his henchmen" for spreading untrue rumours that Mr Cruz cheated on his wife, Heidi.
"Trump demonstrated that when he's scared, when he's losing, his first and natural resort is to go to sleaze and to go to slime," Mr Cruz said.
He added: "He's willing to attack anyone and everyone. And truth has nothing to do with it."
In response to Mr Cruz's comments, Mr Trump's spokeswoman Hope Hicks said: "There is absolutely no truth to this."
And Mr Trump said in a statement that he knows nothing about the allegations.
The accusations are an escalation of the back and forth between the two candidates that began this week, when Mr Trump tweeted that he might "spill the beans" about Heidi Cruz. The tweet was in response to an advertisement from an outside group opposed to Mr Trump's candidacy that featured a risque photo of Mr Trump's wife, Melania.
Mr Cruz, on his Facebook page, accused Mr Trump, who has not held a public event since Monday, of "hiding in Trump Tower" and campaigning by Twitter instead of holding events with voters.
Asked if he plans to vote for Mr Trump if he becomes the party's nominee, Mr Cruz said: "I don't make a habit of supporting people who attack my wife and my family."