Trump says he will boycott final pre-Iowa Republican debate
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, announced the pullout on Tuesday evening, with just 48 hours to go before the debate.
Analysis - Anthony Zurcher, BBC North America reporter
There are plenty of reasons Donald Trump's last-minute withdrawal from the Republican debate could be a bad move.
He's on the verge of winning the Iowa caucuses, so why shake things up now? His past debate performances haven't hurt him, and his most recent was probably his best.
What's to gain from a fight with the most powerful conservative media company in the nation? Already his opponents are blasting him for being afraid of a fight, with Ted Cruz's campaign labelling him "Donald duck".
Yet every time it seems like Mr Trump has made a grievous miscalculation that will sink his campaign, it ends up as either brilliant strategy or his political armour is just too strong.
So maybe this will work out for the New Yorker. He's dominating the headlines once again. And his plan to hold a rally to support wounded veterans, while his opponents aim their criticisms at an empty lectern, could prove a winning contrast.
Did Mr Trump just turn the whole Fox Thursday night event into a "kids' table" debate?
Mr Trump was angered by a statement from a Fox spokesman who poked fun at his 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".
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.
The broadcaster also accused Mr Lewandowski of making veiled threats towards Megyn Kelly.
Mr Trump will 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.
"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'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."
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.
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.