WASHINGTON - White House press secretary Sarah Huckabee Sanders said Tuesday that she couldn't guarantee that the American people will never hear President Donald Trump uttering the n-word on an audio recording, as a former senior White House adviser continued a publicity tour to promote her new book depicting the president as a racist.

The briefing by Sanders came after Trump referred to the former adviser, Omarosa Manigault Newman, as "that dog" in a morning tweet.

"I can't guarantee anything, but I can tell you that the president addressed this question directly," Sanders said. "I can tell you that I've never heard it."

In his tweet earlier Tuesday, Trump praised his chief of staff, John Kelly, for firing Manigault Newman last year. The former reality television star was the highest-ranking black employee in the White House.

"When you give a crazed, crying lowlife a break, and give her a job at the White House, I guess it just didn't work out," Trump said. "Good work by General Kelly for quickly firing that dog!"

Trump's tweet came shortly after Manigault Newman appeared on "CBS This Morning" and released a new recording purportedly of a discussion in October 2016 among campaign aides about how to handle a tape on which Trump is said to have used the n-word.

In tweets Monday night, Trump denied ever using "such a terrible and disgusting word," and his aides have denied having strategized about how to contain the damage if such a tape surfaced. Manigault Newman has said she heard the tape of Trump using the term, which she said dates from Trump's years hosting the NBC reality show "The Apprentice."

Sanders defended Trump's use of the word "dog" in reference to Manigault Newman, saying that the president was simply exasperated with his former aide.

"I think the president is certainly voicing his frustration with the fact that this person has shown a complete lack of integrity, particularly by the actions following her time here at the White House," Sanders said.

During a television appearance later Tuesday, Manigault Newman called Trump "unfit to be in this office and to serve as president of the United States."

"I think that it just shows you that if he would say that publicly, what else would he say about me privately," she said on MSNBC. "He has absolutely no respect for women, for African Americans."

Some Trump critics have argued that the president's recent comments attacking the intelligence of Manigault Newman, Rep. Maxine Waters, D-Calif., CNN host Don Lemon and others reveal a pattern of race-based insults against prominent African Americans.

He has repeatedly referred to Waters as "low IQ" and called Lemon "the dumbest man on television."

At Tuesday's briefing, Sanders responded that "this has absolutely nothing to do with race" and sought to defend Trump by pointing out that he has attacked all types of people.

"The fact is, the president's an equal opportunity person that calls things like he sees it," Sanders said. "He always fights fire with fire, and he certainly doesn't hold back on doing that across the board."

Manigault Newman also disclosed that she has been interviewed by the office of special counsel Robert Mueller, who is probing Russian interference in the 2016 election and possible coordination with the Trump campaign.

"There's a lot of corruption that went on both in the campaign and in the White House and I'm going to blow the whistle on all of it," Manigault Newman said.

Trump has come under fire previously for using derogatory terms to refer to women and African-Americans.

At a debate during the Republican presidential primary season, he was famously asked by moderator Megyn Kelly about his tendency to call women he doesn't like "fat pigs, dogs, slobs, and disgusting animals."

In her book, "Unhinged," Manigault Newman claims the Trump campaign was aware of the existence of the tape from the "Apprentice" period. She describes a phone conversation about how to handle potential fallout with Lynne Patton, then an assistant to Eric Trump, a son of the president; then-Trump spokeswoman Katrina Pierson; and campaign communications director Jason Miller.

The recording played on CBS on Tuesday morning includes the voices of Patton and Pierson. CBS said it had not confirmed the authenticity of the tape.

On the tape, Pierson is heard saying: "I'm trying to find out at least the context it was used in to help us figure out a way to spin it."

Patton then describes having a conversation with Trump about the alleged tape: "I said, 'Well, sir, can you think of anytime this might have happened?' and he said, 'No.'"

"Well, that's not true," Manigault Newman then says on the tape.

Pierson later says: "No, he said it. He is embarrassed."

In a joint statement after Manigault Newman's appearance on CBS, Pierson and Patton said that "no one ever denied the existence of conversations about a reported 'Apprentice' tape" and that they occurred because "Omarosa was obsessed with it."

In a separate statement, Pierson said rumors about an alleged Trump tape were "being circulated by Omarosa and her alone."

"In her secret tape recording of me, it was one of many times that I would placate Omarosa to move the discussion along because I was weary of her obsession over this alleged tape."

In her book, Manigault Newman says she understands that Trump used the slur "multiple times throughout the show's taping during off-camera outtakes, particularly during the first season of 'The Apprentice.'"

In tweets Monday, Trump attacked his former aide as "vicious, but not smart" and claimed that "people in the White House hated her."

His latest attack on Manigault Newman prompted immediate criticism from lawmakers and others.

"The president of the United States is calling a woman of color 'a dog.' How dare he!" Rep. Frederica S. Wilson, D-Fla., said during an interview on CNN. "He has taken this country to its knees."

House Minority Leader Nancy Pelosi, D-Calif., responded to Trump's tweet with one of her own directed toward the president, which said: "#BeBest."

That is the name of the initiative recently launched by first lady Melania Trump that calls for children to speak online with "respect."

Sen. Jeff Flake, R-Ariz., called the language used by Trump "unbecoming of a President of the United States."

"There is no excuse for it, and Republicans should not be okay with it," Flake, a frequent Trump critic, said in a tweet.