US President Donald Trump has reversed his long held stance and admitted to knowing about hush money paid to adult star Stormy Daniels for her silence over an alleged affair in 2006.

Mr Trump acknowledged Thursday night he repaid his personal lawyer for money given to Ms Daniels after claiming previously he didn’t know about the payments.

But the President maintained the money, paid just before the 2016 US election to cut off any claims of an affair, “had nothing to do with the campaign”.

After months of denials, Mr Trump acknowledged his personal lawyer Michael Cohen was reimbursed through a monthly retainer, not campaign funds, for the $US130,000 ($173,300) given to Ms Daniels to stop “false and extortionist accusations” she made about a sexual encounter with him.

Asked aboard Air Force One last month whether he knew about the payment, Mr Trump emphatically said: “No.” Adding he didn’t know why Cohen had made the payment or where he got the money.

Mr Trump on Thursday night said on Twitter the funds were part of a “private agreement”.

In his fullest account to date regarding the payment to Ms Daniels, whose real name is Stephanie Clifford, the President acknowledged the non-disclosure agreement to secure Ms Daniels’ silence, but  forcefully denied the affair.

Mr. Cohen, an attorney, received a monthly retainer, not from the campaign and having nothing to do with the campaign, from which he entered into, through reimbursement, a private contract between two parties, known as a non-disclosure agreement, or NDA. These agreements are…..

— Donald J. Trump (@realDonaldTrump) May 3, 2018

“The agreement was used to stop the false and extortionist accusations made by her about an affair … despite already having signed a detailed letter admitting that there was no affair,” Mr Trump wrote, adding that Ms Daniels and her lawyer had violated it.

“Money from the campaign, or campaign contributions, played no roll (sic) in this transaction.”

The claim of repayment is significant because a payment by Mr Cohen could be seen as an illegal campaign contribution. Mr Trump as candidate would have been permitted to make unlimited personal contributions to his own campaign.

…very common among celebrities and people of wealth. In this case it is in full force and effect and will be used in Arbitration for damages against Ms. Clifford (Daniels). The agreement was used to stop the false and extortionist accusations made by her about an affair,……

— Donald J. Trump (@realDonaldTrump) May 3, 2018

Mr Trump’s admission comes after his new lawyer, and former New York mayor, Rudy Giuliani broke ranks Thursday to reveal Mr Cohen made the payment to Ms Daniels.

During an appearance on Fox News show Hannity, Mr Giuliani said the money had been “funnelled … through the law firm and the President repaid it.”

Asked if Mr Trump knew about the arrangement, the former mayor of New York said: “He didn’t know about the specifics of it, as far as I know. But he did know about the general arrangement, that Michael would take care of things like this, like I take care of things like this for my clients. I don’t burden them with every single thing that comes along. These are busy people.”

Mr Cohen is currently facing a federal criminal investigation in New York in part over the payment to Ms Daniels, with the FBI seizing material from his office and home.

The investigation is an offshoot of the ongoing probe by Special Counsel Robert Mueller into potential collusion between Trump’s campaign and Russia and whether Mr Trump has unlawfully sought to obstruct the probe.

Mr Trump on Thursday said Mr Cohen “received a monthly retainer” from which he entered into the “non-disclosure agreement.”

Mr Trump described such agreements as “very common among celebrities and people of wealth.”

…despite already having signed a detailed letter admitting that there was no affair. Prior to its violation by Ms. Clifford and her attorney, this was a private agreement. Money from the campaign, or campaign contributions, played no roll in this transaction.

— Donald J. Trump (@realDonaldTrump) May 3, 2018

-with AAP