White House spokeswoman Sarah Huckabee Sanders says she cannot guarantee that President Donald Trump has never used a racial slur.

Sanders said, "I haven't been in every single room," when asked if she can say with certainty that Trump has never used the N-word.

Ex-Trump aide Omarosa Manigault Newman has alleged she has heard Trump on tape using the slur.

Trump said Monday on Twitter that he doesn't "have that word in my vocabulary, and never had."

Sanders says she "can't guarantee" Trump has never used the word, but calls Manigault Newman's claims "salacious and ridiculous."

Trump escalated his messy clash with former aide Manigault Newman on Tuesday, referring to the longtime colleague, who had been the top African-American in his White House, as "that dog!"

Sanders said Manigault Newman has "shown a complete lack of integrity" with her criticism of Trump in her new book.

Sanders said Tuesday that Trump's tweets referring to Manigault Newman as "crazed" and a "dog" reflect his "frustration" with her comments. Manigault Newman has responded that Trump has "absolutely no respect" for women or African-Americans.

Sanders says Trump hired Manigault Newman as an assistant to the president because he "wanted to give her a chance." She was a contestant on his reality show "The Apprentice" and a former campaign aide.

Manigault Newman has been releasing audio recordings of private White House conversations as part of her book roll-out tour. She was fired in December.

The pressure on Manigault Newman increased Tuesday as the Trump presidential campaign filed arbitration action against her, alleging a breach of a confidentiality agreement. A campaign official said the action was filed with the American Arbitration Association.

Trump tweeted a barrage of insults Tuesday morning as Manigault Newman continued promoting her White House tell-all and releasing secret audio recordings. Her book paints a damning picture of Trump, including her claim that he used racial slurs on the set of his reality show "The Apprentice."

"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!" John Kelly is White House chief of staff.

While Trump trades in insults on a near daily basis, deeming Manigault Newman a "dog" was a stunning move in a row that touched on several sensitive issues in Trump's White House, including a lack of racial diversity among senior officials, security concerns — Manigault Newman taped her firing in the White House Situation Room — and extraordinary measures such as non-disclosure agreements to keep ex-employees quiet.

Manigault Newman said in an interview on MSNBC Tuesday that Trump's latest attack on her was evidence that he has "absolutely no respect" for women and African-Americans.

"If he would say that publicly, what else would he say about me privately," she asked. She called the president "unfit to be in this office."

Trump has pushed back against Manigault Newman's claim that she had heard an audiotape of him using the N-word. He tweeted that he had received a call from the producer of "The Apprentice" assuring him "there are NO TAPES of the Apprentice where I used such a terrible and disgusting word as attributed by Wacky and Deranged Omarosa."

Trump insisted, "I don't have that word in my vocabulary, and never have." He said Manigault Newman had called him "a true Champion of Civil Rights" until she was fired.

Manigault Newman, the former White House liaison to black voters, writes in her new memoir that she'd heard such tapes existed. She said Sunday that she had listened to one after the book closed.

On CBS Tuesday, Manigault Newman released another audio recording that she said showed campaign workers discussing an alleged recording of Trump using the racial slur. The White House and the campaign did not immediately respond to questions.

One of the people allegedly featured on the tape is Katrina Pierson, an adviser to Trump's re-election campaign who served as a spokeswoman for his 2016 campaign. Pierson has said she never heard Trump use this type of language and said on Fox that the only person she heard talking about a tape was Manigault Newman. The tape appears to show Pierson saying of Trump: "He said it. He's embarrassed."

Asked if the book can be backed up by email or recordings, Manigault Newman said on CBS that every quote in the book "can be verified, corroborated and it's well documented," suggesting she may have more information to release.

The dispute has been building for days as Manigault Newman promotes her memoir "Unhinged," which comes out officially Tuesday.

In a series of interviews, Manigault Newman has also revealed two audio recordings from her time at the White House, including portions of a recording of her firing by Kelly, which she says occurred in the high-security Situation Room, and a phone call with Trump after she was fired.

Manigault Newman says she has more recordings. Asked on MSNBC's "Hardball" if special counsel Robert Mueller — investigating possible coordination between the Trump campaign and Russia — would be interested in any of them, she said, "If his office calls again, anything they want, I'll share."

Trump officials and a number of outside critics denounced the recordings as a serious breach of ethics and security — and White House aides worried about what else Manigault Newman may have captured in the West Wing.

The tape recording appears to show Trump expressing surprise about her firing, saying "nobody even told me about it." But Manigault Newman said he "probably instructed General Kelly to do it."

On Twitter, Trump declared Monday that she had been "fired for the last time," a reference to her appearances on his reality TV show. He said Kelly had called her a "loser & nothing but problems," but he himself had tried to save her job — because he liked her public comments about him.

"I told him to try working it out, if possible, because she only said GREAT things about me - until she got fired!" Trump tweeted.

Responding on NBC, Manigault Newman said, "I think it's sad that with all the things that's going on in the country that he would take time out to insult me and to insult my intelligence."

She added, "This is his pattern with African-Americans."

First lady Melania Trump, meanwhile, is disappointed that Manigault Newman "is lashing out and retaliating in such a self-serving way, especially after all the opportunities given to her by the President," said White House spokeswoman Stephanie Grisham.

Manigault Newman's exit does highlight the lack of diversity among Trump's top aides. She was the highest-ranking African-American on the White House staff. She said on NBC that in her absence "they're making decisions about us without us."

Trump's battle with Omarosa underscores the racial tensions that have defined his presidency. He notably blamed "both sides" for violent clashes between white supremacists and counterprotesters in Charlottesville, Virginia, a year ago and has questioned the intelligence of other prominent black figures including California Rep. Maxine Waters, basketball star LeBron James and TV journalist Don Lemon. He also has targeted black NFL players for kneeling in social protest during the national anthem.

Manigault Newman also alleges that Trump allies tried to buy her silence after she left the White House, offering her $15,000 a month to accept a "senior position" on his 2020 re-election campaign along with a stringent nondisclosure agreement.

The offer raises fresh questions about the ways that White House aides are being offered safe landing spots after they leave. For example, Trump's former personal aide John McEntee, who was removed from his job in April, went to the campaign.

Trump tweeted Monday that Manigault Newman has a "fully signed Non-Disclosure Agreement!"

It was not clear exactly what he was referring to. White House Counselor Kellyanne Conway said Sunday on ABC that there are "confidentiality agreements" in the West Wing. And Trump's campaign said that in the 2016 race she "signed the exact same NDA that everyone else on the campaign signed, which is still enforceable."

Meanwhile, Trump's attorney, Rudy Giuliani, said on "Fox and Friends" Monday that Manigault Newman may have broken the law by recording private conversations inside the White House.

"She's certainly violating national security regulations, which I think have the force of law," Giuliani said.

But experts in national security and clearance law said that, while she seriously violated rules — and would likely be barred from ever being granted a security clearance — she probably didn't break any law unless the conversations she recorded were classified.

In the recording with Kelly, which Manigault Newman quotes extensively in her new book, Kelly can be heard saying that he wants to talk with her about leaving the White House.

"It's come to my attention over the last few months that there's been some pretty, in my opinion, significant integrity issues related to you," Kelly is heard saying, before adding that if she makes it a "friendly departure" then she can "go on without any type of difficulty in the future relative to your reputation."

Manigault Newman said she viewed the conversation as a "threat" and defended her decision to covertly record it and other White House conversations, saying otherwise "no one" would believe her.

Associated Press writers Darlene Superville and Hope Yen contributed to this report.