A lawyer for adult film star Stormy Daniels filed a court motion today seeking to question US President Donald Trump under oath about the alleged affair between them.

If successful, it would be the first deposition of a sitting president since 1998 when Bill Clinton was forced to give evidence about his conduct with women, the Daily Telegraph reports.

Michael Avenatti, the lawyer, filed the motion in court in Los Angeles and is seeking up to two hours of the President's time to question him.

He is seeking sworn evidence from both Trump, and Trump's personal lawyer Michael Cohen, about a US$130,000 payment made to the porn star, whose real name is Stephanie Clifford.

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The payment was made days before the 2016 presidential election as part of a non-disclosure agreement which Clifford is seeking to invalidate.

Avenatti said he wants to question Trump to establish if he knew about the money, referring to as a "hush agreement".

He said: "We're looking for sworn answers from the President and Mr Cohen about what they knew, when they knew it and what they did about it."

Avenatti said that "in every case you always have to be open to settlement" but "at this point we don't see how this case would possibly be settled".

In a statement David Schwartz, a lawyer representing Cohen, called it a "reckless use of the legal system in order to continue to inflate Michael Avenatti's deflated ego and keep himself relevant".

The White House, which has said Trump denies the relationship, did not respond to requests for comment.

A hearing before a judge in Los Angeles to decide whether Trump must give evidence is set for April 30.

Clinton had to do so in 1998 during Paula Jones' sexual harassment case.

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At the time the US Supreme Court ruled that a sitting president was not immune from civil litigation on something that happened before taking office and was unrelated to the office.

Stormy Daniels during her 60 Minutes interview. Photo / AP
Stormy Daniels during her 60 Minutes interview. Photo / AP