Representatives for US President Donald Trump have launched legal action against former aide Omarosa Manigault Newman, claiming she breached a secrecy agreement.

Mr Trump’s campaign is filing the claim with the America Arbitration Association in New York, saying her explosive new book, Unhinged, and media tour breaches a 2016 confidentiality agreement.

Ms Manigault Newman has acknowledged signing a confidentiality agreement with the campaign in 2016.

“President Trump is well known for giving people opportunities to advance in their careers and lives over the decades, but wrong is wrong, and a direct violation of an agreement must be addressed and the violator must be held accountable,” Donald J. Trump for President, Inc. said in a statement.

The former reality TV star’s book, released in the US on Wednesday morning (AEST), alleges that after she was fired from the White House in December, she was offered a $US15,000 ($20,600) per month position with the Trump re-election effort in exchange for signing a new confidentiality agreement.

Ms Manigault Newman said she declined that offer.

Earlier, Mr Trump called his former aide and reality TV co-star “that dog” in an extraordinary Twitter attack.

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!

— Donald J. Trump (@realDonaldTrump) August 14, 2018

The post was a reference to Mr Trump’s White House chief of staff, retired general John Kelly, who fired Mr Manigault Newman in Situation Room conversation she said she interpreted as a “threat”.

Mr Trump has also retaliated after Ms Manigault Newman claimed she had heard an audio tape of him using racial slurs while they worked on The Apprentice.

Mr Manigault Newman has released several audio recordings from her time at the White House, including a phone conversation with Mr Trump in which he claims nobody told him she had been fired.

A new recording released to US broadcaster CBS on Tuesday purports to document Trump campaign aides speaking during the 2016 election about how to deal with the potential fallout from an older allegation that Mr Trump had said the N-word.

Mr Trump refuted the claims, tweeting 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.”

The President insisted: “I don’t have that word in my vocabulary, and never have.”

He said Ms Manigault Newman had called him “a true Champion of Civil Rights” – until she was fired.

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

-with AAP