MARSHALLTOWN, Iowa/IOWA CITY, Iowa (Reuters) - U.S. Republican presidential hopeful Donald Trump withdrew on Tuesday from a debate with party rivals this week out of anger at host Fox News FOXA.O, leaving the last encounter before Iowa's pivotal nominating contest without the front-runner.

Trump's campaign manager, Corey Lewandowski, told reporters after a combative news conference held by the candidate that Trump would definitely not be participating in the debate scheduled for Thursday in Des Moines, Iowa, and co-hosted by Google GOOGL.O.

During the news conference before he addressed a large crowd in Marshalltown, Iowa, Trump expressed irritation that Fox News planned to leave in place as a moderator the anchor Megyn Kelly, whose questioning of Trump at a debate last August angered him.

He also expressed displeasure at a Fox News statement on Monday night saying Trump would have to learn sooner or later that “he doesn’t get to pick the journalists” and that “we’re very surprised he’s willing to show that much fear about being questioned by Megyn Kelly.”

“I was all set to do the debate, I came here to do the debate. When they sent out the wise-guy press release done by some PR person along with (Fox News Chairman) Roger Ailes, I said: ‘Bye bye, OK’”

“Let’s see how much money Fox makes without me in the debate,” the billionaire businessman added.

Trump has been engaged in a public spat with Fox News since the network hosted the first debate and Kelly asked Trump about his treatment of woman, prompting a stream of insults from the candidate.

The debate is scheduled for just days before Iowa’s caucuses on Monday, the first nominating contest for the Nov. 8 presidential election.

Trump’s campaign announced that instead of participating in the debate, he would hold a fundraiser for “Veterans and Wounded Warriors.”

Fox News responded by releasing a statement charging Trump’s campaign manager with threatening Kelly, saying during a call Lewandowski had referred to her “rough couple of days” after the previous debate she moderated and added that he would “hate to have her go through that again.”

“We can’t give in to terrorizations toward any of our employees,” Fox said in a statement.

The network added that Trump remains welcome to participate in the Thursday night debate.

Trump’s Republican rivals quickly criticized him for opting out of the debate.

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“The fact that Donald is now afraid to appear on the debate stage, that he doesn’t want his record questioned, I think that reflects a lack of respect for the men and women on Iowa,” Texas Senator Ted Cruz, who is in a tight race with Trump for first place in the state, said on Mark Levin’s radio program.

“If Donald is afraid of Megyn Kelly, I would like to invite him on your show to participate in a one-on-one debate between me and Donald, mano-a-mano,” Cruz said, adding: “If he thinks Megyn Kelly is so scary, what exactly does he think he’d do with Vladimir Putin?”

Former Florida Governor Jeb Bush criticized Trump on Twitter, saying: “exactly” in response to a conservative commentator who cast doubt on whether Trump could run against Democratic front-runner Hillary Clinton if he were afraid of Kelly.

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DEMOCRATS DEBATE ADDITIONAL DEBATE

In the Democratic contest, news channel MSNBC and the New Hampshire Union Leader newspaper sketched out plans to host a debate in New Hampshire among Clinton and challengers Bernie Sanders and Martin O’Malley, a few days before the state’s primary election on Feb. 9.

But the Democratic National Committee raised doubts about whether it would proceed, saying in a statement it had no plans to sanction the debate.

It left open the question of whether it would punish any participants by excluding them from the two remaining sanctioned debates.

Spokesmen for Clinton, the former secretary of state who leads most polls, and O’Malley, a former Maryland governor, said their candidates would be happy to take part, at least in theory.

The New York Times quoted the campaign manager for Sanders as saying the Vermont senator would sit out the unsanctioned debate.

RATINGS BONANZA

Trump’s blunt-spoken candidacy has boosted ratings for the Republican presidential debates. The August debate on Fox News drew 24 million viewers, a record for a presidential primary debate and the highest non-sports telecast in cable TV history.

But a boycott could prove risky for Trump as Iowa Republicans seek to take one more look at who they want as their presidential candidate. Rivals like Cruz, Florida Senator Marco Rubio, Bush, and retired neurosurgeon Ben Carson could reap the benefits.

“How many debates do you have to do?” Trump told reporters. “The Democrats are finished with their debates. ... The Republicans go on forever and ever and ever with debates. We have people on the stand who have zero (percentage points in the poll), who have one, who have nothing. So it’s time that somebody plays grown up.”

At his campaign event in Marshalltown, Trump expressed confidence in his position in the race, saying if he were to win Iowa, he could “run the table” and roll up subsequent victories in New Hampshire, South Carolina and beyond.

“Iowa is very important. So you’ve got to get out, you’ve got to get out and caucus,” he told his supporters.