"I am done with the lying," Cohen said. "I am done being loyal to President Trump."

He added: "I will not be the villain of this story."

Cohen was sentenced on Wednesday to three years in federal prison after pleaded guilty to several charges, including campaign finance violations and lying to Congress. Prosecutors have said Trump directed Cohen to arrange the payments to buy the silence of porn actress Stormy Daniels and former Playboy model Karen McDougal in the run-up to the 2016 campaign.

The decisions to pay off Daniels, who alleged she had sex with a married Trump in 2006, during the run-up to the 2016 election was made soon after an old Access Hollywood tape surfaced, in which Trump was heard talking about groping and trying to have sex with women, Cohen said.

"He was very concerned about how this would affect the election," Cohen said.

The hush money wasn't initially reported on campaign finance documents and, in any case, far exceeded the legally acceptable amount for in-kind contributions. The federal limit on individual contributions is $US2,700.

As to whether Trump knew it was wrong to make the payments, Cohen said: "First of all, nothing at the Trump organisation was ever done unless it was run through Mr Trump. He directed me to make the payments, he directed me to become involved in these matters."

Trump has denied directing Cohen to break the law and has asserted in a barrage of tweets over the last several weeks that Cohen is a "liar" who cut a deal in order to get a reduced prison sentence and to help himself and his family.

Loyalty has long been a core value for Trump, who has been stung by the behaviour of Cohen and other former associates who have dissociated themselves from the President, intent on saving themselves. That list also includes former White House staffer Omarosa Manigault Newman and former National Security adviser Michael Flynn.

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"He knows the truth. I know the truth. Others know the truth," Cohen said. "And here is the truth: people of the United States of America, people of the world, don't believe what he is saying. The man doesn't tell the truth. And it is sad that I should take responsibility for his dirty deeds.

"Instead of him taking responsibility for his actions, what does he do? He attacks my family."

Cohen insists that Trump is a different person now than when he was running his real estate empire in New York and said he believes the pressure of being the President of the United States is "much more than he thought it was going to be".

Daniels, whose real name is Stephanie Clifford, was paid $US130,000 as part of a nondisclosure agreement that was signed days before the 2016 election and she's currently suing to dissolve that contract.

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In August 2016, the parent company of the tabloid National Enquirer reached a $US150,000 deal to pay McDougal for her story of a 2006 affair, which it never published, a tabloid practice known as catch and kill.

Cohen insisted he just reviewed the McDougal deal and said the payment was negotiated directly between Trump and David Pecker, the chief executive officer of the tabloid's parent company.

Both Cohen and American Media Inc now say they made hush-money payments were to help Trump's 2016 White House bid. The US attorney's office in Manhattan reached a non-prosecution agreement with the company.

In a separate case, Cohen pleaded guilty to lying to Congress about his work on a possible Trump real estate project in Moscow and said he did so to be consistent with Trump's "political messaging".

The charges in that case were brought by special counsel Robert Mueller's office and Mueller's prosecutors have said Cohen has provided key information in their investigation. Cohen has said he is continuing to cooperate with investigators in the Russia probe, which the President has repeatedly called a "witch hunt".

AP