US President Donald Trump calls ex-'Apprentice' star turned White House aide a 'dog'

US President Donald Trump on Tuesday called former White House aide Omarosa Manigault Newman a "dog" and his campaign took legal action against her as the two former reality TV stars escalated their public feud.

The spat came as Manigault Newman, a former contestant on Trump's "The Apprentice," publicly released more recordings from her time in Trump's orbit as she promoted her tell-all book, "Unhinged," describing her year at the White House. She was fired in December.

In the book, she accused Trump of making derogatory statements about African-Americans, Filipinos and other minorities, as well as exhibiting "forgetfulness and frustration."

"His mental decline could not be denied," wrote Manigault Newman, who had been one of the Republican president's most prominent black supporters.

The White House did not respond to a request for comment.

On Twitter on Tuesday, Trump wrote, "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. Good work by General Kelly for quickly firing that dog!"

In recent days, Manigault Newman has released audio of her firing by White House Chief of Staff John Kelly and of a call from Trump in which he says he did not know about her dismissal.

On Tuesday, CBS News released another recording it said was unverified but appeared to be Manigault Newman and several Trump campaign aides in October 2016 discussing the potential fallout from a tape of Trump using a racial epithet during the taping of "The Apprentice."

CBS News' parent company, CBS Corp, owns Simon and Schuster Inc, which published her book. In it, Manigault Newman describes the recorded conversation as being a conference call held on Oct. 11, 2016.

Trump's campaign, which is gearing up for his 2020 re-election run, has filed an arbitration against Manigault Newman for breaching her 2016 confidentiality agreement, a Trump campaign official said on Tuesday.

Asked about the pact, she told MSNBC: "I don't believe that I violated it," adding that she would leave that to lawyers to sort out.

Trump on Monday denied the existence of any tape from "The Apprentice" in which he used the racial epithet, citing the show's former producer, Mark Burnett. Some of the aides on the latest tape also denied the conversation.

Reuters could not verify any of the recordings, and representatives for Burnett and his production company did not immediately respond to requests for comment.

Critics condemned Trump's tweet for what they said were racial and sexist undertones.

"The president of the United States is calling a woman of color a dog? ... How dare he call anyone a dog?" Democratic U.S. Representative Frederica Wilson, who is also an African-American, told CNN.

U.S. Senator Jeff Flake, a frequent Trump critic, called the president's language "unbecoming" and said fellow Republicans "should not be okay with it."

Asked whether Trump's language was appropriate, White House senior counselor Kellyanne Conway did not answer directly but told Fox News she had never heard Trump "issue a racial slur about anyone."

Trump brought on Manigault Newman, previously known for repeatedly being fired on NBC's "The Apprentice," as director of communications for the White House Office of Public Liaison.

Manigault Newman has dismissed any legal concerns about taping conversations. On Monday, she told MSNBC that, if asked, she would give her recordings to the U.S. Special Counsel's Office investigating alleged Russian interference in the 2016 presidential election and possible collusion by the Trump campaign.

Russia has denied meddling in the election and Trump has repeatedly called the probe by Special Counsel Robert Mueller a witch hunt.