The attorney representing a porn star who is suing Donald Trump has said that the US President's personal lawyer had a restraining order issued against her and continues to pressurize her to keep silent, a media report said.

Stephanie Clifford, also known as Stormy Daniels, has filed a lawsuit against Trump in which she cites multiple instances of the President's legal counsel, Michael Cohen, working to keep her from speaking out about an alleged sexual encounter, the CNN report said.

Clifford's attorney Michael Avenatti said a private mediator issued the temporary restraining order against her on behalf of Cohen on February 27, and has cautioned Clifford to keep quiet as recently as Wednesday.

"Earlier today (Wednesday), Cohen through his attorney, (Lawrence) Rosen, further threatened my client in an effort to prevent her from telling the truth about what really happened," Avenatti told CNN on Wednesday night.

"We do not take kindly to these threats, nor will we be intimidated."

According to the legal complaint filed in California state court, Clifford is claiming that a non-disclosure agreement is void because Trump never signed it himself.

The "hush" agreement allegedly regards an affair involving the two several years before Trump was in office.

Just weeks before the 2016 election, Cohen paid Clifford $130,000, an admission he made in a statement last month.

"Despite Trump's failure to sign the Hush Agreement, Cohen proceeded to cause $130,000.00 to be wired to the trust account of Clifford's attorney. He did so even though there was no legal agreement and thus no written nondisclosure agreement whereby  Clifford was restricted from disclosing the truth about Trump," the document stated.

On Wednesday, White House press secretary Sarah Sanders fielded questions about the payment and said Trump did not know about it, reports CNN.

"Not that I'm aware of," Sanders responded when pressed on whether Trump knew about the payment.

"Anything beyond what I've already given you, I would refer you to the President's outside counsel."

Sanders also said that "the arbitration was won in the President's favour", admitting for the first time that a non-disclosure agreement did exist, and that the President is involved.

When asked about the comments Sanders made regarding the arbitration, Avenatti told CNN: "President Trump hasn't won anything relating to Clifford."