US President Donald Trump has admitted for the first time Michael Cohen represented him in the “crazy Stormy Daniels deal”, after previously denying any knowledge of a hush payment his personal lawyer arranged with the adult star.

For weeks, Mr Trump has told reporters he had no knowledge of a $US130,000 payment Mr Cohen made to Ms Daniels before the 2016 presidential election in exchange for her silence about an alleged sexual affair they had more than a decade ago.

But in an interview with TV show Fox & Friends on Friday morning (AEST) the President conceded Mr Cohen acted on his behalf with Ms Daniels.

“He represents me, like with this crazy Stormy Daniels deal, he represented me,” Mr Trump said.

“From what I see, he did absolutely nothing wrong. There were no campaign funds going in,” he said.

The fresh admission comes as federal prosecutors in New York investigate Mr Cohen’s personal business dealings.

Mr Trump sought to distance himself from his decade-long lawyer, saying Mr Cohen was one of his “many attorneys” and that he had been told he was not involved in the FBI investigation.

“This doesn’t have to do with me. Michael is a businessman. He’s got a business. He also practices law,” Mr Trump said.

“And they’re looking at something having to do with his business. I have nothing to do with his business.”

Asked how much legal work Cohen did for him, Mr Trump said: “As a percentage of my overall legal work, a tiny, tiny little fraction.”

In a filing in Los Angeles federal court on Wednesday, Mr Cohen said he decided to assert his constitutional right not to give evidence that may incriminate him after the FBI raided his home, office and hotel room two weeks ago.

“Based on the advice of counsel, I will assert my 5th Amendment rights in connection with all proceedings in this case due to the ongoing criminal investigation by the FBI and US Attorney for the Southern District of New York,” Mr Cohen wrote in the filing.

The Fifth Amendment to the US Constitution states that no individual can be “compelled in any criminal case to be a witness against himself”.

By asserting that right, Mr Cohen can avoid revealing information in Ms Daniels’ civil lawsuit that could aid federal investigators in the criminal probe of his business dealings.

Mr Trump earlier in April told reporters aboard Air Force One his did not know about the hush payment to Ms Daniels, or where Mr Cohen had got the money.

When asked why Mr Cohen made the payment, the president said: “You’ll have to ask Michael Cohen. Michael is my attorney. You’ll have to ask Michael.”

-with AAP