NEW YORK >> Fox News chief Roger Ailes said Tuesday that Donald Trump owes the network’s Megyn Kelly an apology for an unprovoked Twitter attack that “is as unacceptable as it is disturbing.”

The Republican presidential front-runner-turned-TV-critic had welcomed Kelly back from a vacation Monday night by tweeting that he liked her show better while she was away. Trump said Kelly “must have had a terrible vacation” because “she’s really off her game.” He retweeted a message that referred to her as a bimbo.

“Megyn Kelly represents the very best of American journalism and all of us at Fox News Channel reject the crude and irresponsible attempts to suggest otherwise,” said Ailes, the Fox News Channel chairman. “I could not be more proud of Megyn for her professionalism and class in the face of all of Mr. Trump’s verbal assaults.”

Trump has been attacking Kelly ever since her tough questioning of him during the first GOP presidential debate, seen by 24 million people on Fox on Aug. 6. A day after the debate, he said Kelly had “blood coming out of her eyes, blood coming out of her wherever.”

That led to a private, clear-the-air conversation between Ailes and Trump two weeks ago, but that clearly hasn’t led to peace.

In his tweets, Trump repeated his contention that Kelly, host of a prime-time Fox show and one of the network’s biggest stars, was sent on an unplanned vacation that ended Monday. Fox said her time off had been scheduled long before the debate. Trump also tweeted that Kelly was afraid to confront a guest, Dr. Cornel West, and that she had “no clue” on immigration.

Ailes again backed Kelly for her questioning during the debate, which he said was tough but fair.

“Donald Trump rarely apologizes, although in this case, he should,” Ailes said. “We have never been deterred by politicians or anyone else attacking us for doing our job, much less allowed ourselves to be bullied by anyone and we’re certainly not going to start now.”

Some of Kelly’s Fox colleagues also came to her defense. Bret Baier, who moderated the debate with Kelly and Chris Wallace, tweeted that “this needs to stop.” Brian Kilmeade said on “Fox & Friends” that Trump’s comments bothered him personally.

“We are all friends with Donald Trump, but he is totally out of bounds reigniting that fight,” Kilmeade said. “I don’t know if he’s trying to get ratings out of that or poll numbers, but he’s not going to be successful.”