Donald Trump has said he will boycott the final Republican presidential debate before the Iowa caucuses.
The Republican frontrunner had clashed with the moderator, Megyn Kelly of Fox News, in the first debate in August and says she would not treat him fairly.
Fox News accused Mr Trump of vicious attacks on Kelly and making demands that she be removed. Capitulating would “violate all journalistic standards”.
“We can’t give in to terrorisations toward any of our employees,” it said.
Mr Trump’s campaign manager, Corey Lewandowski, had announced the pullout on Tuesday evening, with just 48 hours to go before the debate.
Fox News accused Mr Lewandowski of making threats towards Megyn Kelly.
Its statement read: “In a call on Saturday with a Fox News executive, Lewandowski stated that Megyn had a ‘rough couple of days after that last debate’ and he ‘would hate to have her go through that again’.
“Lewandowski was warned not to level any more threats, but he continued to do so.”
Fox said Mr Trump would still be welcome at the debate and would be treated fairly but “he can’t dictate the moderators or the questions”.
“We’re not sure how Iowans are going to feel about him walking away from them at the last minute,” Fox said.
Mr Trump had earlier lashed out at Kelly, claiming she had been “toying” with him.
He said he intended to hold a separate Iowa event at the same time as the debate to raise money for wounded veterans. Iowa hosts the nation’s opening presidential primary contest on Monday.
“With me, they’re dealing with somebody that’s a little bit different,” he said.
“They can’t toy with me like they toy with everybody else. Let them have their debate and let’s see how they do with the ratings.”
Mr Trump had also been angered by an earlier statement from a Fox spokesman who poked fun at the threats to boycott the debate.
The statement had read: “We learned from a secret back channel that the Ayatollah and Putin both intend to treat Donald Trump unfairly when they meet with him if he becomes president – a nefarious source tells us that Trump has his own secret plan to replace the Cabinet with his Twitter followers to see if he should even go to those meetings.”
Mr Trump said it was “written by a child”.
Mr Trump’s pullout prompted his closest rival, Texas Senator Ted Cruz, to challenge him to a one-on-one debate.
Mr Cruz said: “Apparently Megyn Kelly is really, really scary. And you know, Donald is a fragile soul.”
‘With or without’
On Tuesday night’s airing of her Fox News show, The Kelly File, Kelly said the debate would “go on with or without Mr Trump”.
In the first Republican TV debate back in August, Mr Trump accused her of asking “ridiculous” questions.
In a statement widely perceived to be a reference to menstruation, something Mr Trump later denied, he said: “You could see there was blood coming out of her eyes, blood coming out of her wherever.”
The Republican National Committee (RNC) said Mr Trump’s latest decision to withdraw was up to him.
“Obviously we would love all of the candidates to participate, but each campaign ultimately makes their own decision what’s in their best interest,” said RNC chief strategist Sean Spicer.
Mr Trump’s decision leaves seven other candidates in the debate: Mr Cruz, Florida Senator Marco Rubio, retired neurosurgeon Ben Carson, former Florida Governor Jeb Bush, New Jersey Governor Chris Christie, Ohio Governor John Kasich and Kentucky Senator Rand Paul.
Mr Trump has garnered media attention with provocative actions and statements, including a call for a temporary ban on all Muslim immigrants.