Donald Trump has tweeted to dismiss a sketch of a man who the adult film actress Stormy Daniels said threatened her on the president's behalf.
President Trump claimed the man was "nonexistent" and called the sketch "a total con job".
The reference is his first on Twitter to the Stormy Daniels affair, following a long and uncharacteristic silence.
Ms Daniels, real name Stephanie Clifford, alleges that she had a sexual relationship with Mr Trump in 2006.
During a recent television interview, she said she was threatened in 2011 in a Las Vegas car park, while she was with her infant daughter, and told to keep quiet about the alleged affair.
"A guy walked up on me and said to me, 'Leave Trump alone, forget the story'," she told the 60 minutes programme.
"And he leaned around and looked at my daughter and said, 'That's a beautiful little girl, it would be a shame if something happened to her mom'."
On Tuesday, Ms Daniels and her attorney, Michael Avenatti, produced a composite-style sketch of the man and offered a reward of $100,000 (£70,000) to anyone who could identify the man. On Wednesday Mr Avenatti raised the reward to $131,000.
That sum may be a reference to a $130,000 payment to Ms Daniels by Mr Trump's lawyer, Michael Cohen, during the 2016 presidential campaign. Ms Daniels accepted the sum in return for signing a non-disclosure agreement.
Ms Daniels is now suing the president in an attempt to extricate herself from the non-disclosure agreement, which she alleges is invalid because he did not sign it personally.
Mr Trump has reportedly been advised not to make public statements about Ms Daniels.
But he turned to Twitter on Wednesday to repost a tweet by a supporter which suggested the sketch resembled the actress's ex-husband, adding his own remarks.
Ms Daniels' lawyer, Mr Avenatti, who has not shied away from publicity over the case or from goading Mr Trump, responded to the president's tweet with his own, writing: "In my experience, there is nothing better in litigation than having a completely unhinged, undisciplined opponent who is prone to shooting himself in the foot."
Speaking to the New York Times on Wednesday, Mr Avenatti said the president's tweet could lead to a defamation lawsuit, as he had "now effectively called my client a liar".
Ms Daniels appeared in an interview with ABC's The View programme on Tuesday, a day after she attended a federal court hearing where Mr Cohen was seeking to limit the ability of prosecutors to review documents seized in recent raids on his home, office and hotel room.
Mr Cohen is being investigated for criminal wrongdoing, and Ms Daniels said she wanted to be present for anything that might be relevant to her.
Legal analysts have said that Mr Cohen's $130,000 payment to Ms Daniels could have violated the rules on financing Mr Trump's 2016 presidential campaign.