A secret recording is said to have revealed the moment one of United States President Donald Trump's closest advisers was given the boot from the White House.

Omarosa Manigault-Newman, a controversial Apprentice contestant who became a White House staffer before her unexpected resignation in December, provided the controversial audio to NBC.

However, the explosive recordings reveal her sacking was a far cry from Mr Trump's reality TV days, when he would cock his finger like a gun and mercilessly proclaim, "You're fired!" — before sending the contestant home with a wheeled suitcase.

Instead, Ms Manigault-Newman told NBC she was taken to one of the White House's most secure and secretive rooms — the Situation Room — and quietly told what was happening.

In one clip aired by the network, White House chief of staff John Kelly can be heard saying she would be "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," Mr Kelly can be heard saying.

The recordings are being slammed as a major security breach and there are now calls from senior Republicans for Ms Manigault-Newman — who has painted a damning picture of Mr Trump in her new book — to be prosecuted.

Mr Kelly can be heard in another clip telling the former Apprentice star a smooth exit would help her reputation, a suggestion Ms Manigault-Newman told NBC she took as a threat.

He can also be heard saying she can look at her time at the White House as a year of "service to the nation" and referring to potential "difficulty in the future relative to your reputation".

"I think it's important to understand that if we can make this a friendly departure we can all be, you know, you can look at your time here in the White House as a year of service to the nation, and then you can go on without any type of difficulty in the future relative to your reputation," Mr Kelly said on the tape.

In another secret clip, aired on NBC, Ms Manigault-Newman can be heard asking if Mr Trump was "aware of what's going on" and Mr Kelly interjecting and saying, "This is a non-negotiable discussion."

"I don't want to negotiate," Ms Manigault Newman replied. "I just, I've never talked — had a chance to talk to you, General Kelly, so if this is my departure, I'd like to have at least an opportunity to understand."

General Kelly responded, "We can, we can talk another time. This has to do with some pretty serious integrity violations. So I'll let it go at that. So the staff and everyone on the staff works for me, not the President."
In response to the bombshell recordings, White House press secretary Sarah Sanders has taken aim at Ms Manigault-Newman.

"The very idea a staff member would sneak a recording device into the White House Situation Room, shows a blatant disregard for our national security — and then to brag about it on national television further proves the lack of character and integrity of this disgruntled former White House employee," Ms Sanders said.

The Situation Room is a Sensitive Compartmented Information Facility, or SCIF, and staff are not permitted to bring in mobile phones or other recording devices.

"I've never heard of a more serious breach of protocol," said Ned Price, who served as spokesman of the National Security Council in the Obama administration. "Not only is it not typical, something like this is unprecedented.

"The Situation Room is the innermost sanctum of a secure campus."

Ronna McDaniel, the chairwoman of the Republican National Committee, called Ms Manigault-Newman's recording "wildly inappropriate" and suggested she may have violated the law.

"Secretly recording conversations in the Situation Room isn't just wildly inappropriate, it's a threat to our national security. If she broke federal law, she should be prosecuted," Ms McDaniel tweeted.

However, Ms Manigault-Newman said she viewed the comment as a "threat" and defended her decision to covertly record it and other White House conversations, describing it as a form of protection.

"If I didn't have these recordings, no one in America would believe me," she said.

In her book, Ms Manigault-Newman paints a damning picture of President Donald Trump, including claiming that tapes exist of him using the N-word as he filmed his The Apprentice reality series, on which she co-starred.

The White House has tried to discredit the book, with Mr Trump on Saturday labelling Ms Manigault Newman a "low-life".

White House counsellor Kellyanne Conway also questioned Ms Manigault Newman's credibility in an interview on Sunday on ABC's This Week.

"The first time I ever heard Omarosa suggest those awful things about this President are in this book," she said, noting Ms Manigault Newman "is somebody who gave a glowing appraisal of Donald Trump the businessman, the star of the The Apprentice, the candidate and, indeed, the President of the United States".

Ms Manigault-Newman had indeed been a staunch defender of the President for years, but she now says she was "used" by Mr Trump for years, calling him a "con" who "has been masquerading as someone who is actually open to engaging with diverse communities" and is "truly a racist".

"I was complicit with this White House deceiving this nation," she said. "I had a blind spot where it came to Donald Trump."