US first lady Melania Trump has demanded Hunter Biden retract comments linking her to sex trafficker Jeffrey Epstein or she will sue him.

Trump has taken issue with two comments by Biden, son of former US president Joe Biden, in an interview this month with British journalist Andrew Callaghan.

He alleged Epstein introduced the first lady to now-President Donald Trump.

In a letter to Biden, Melania Trump’s lawyer Alejandro Brito said the statements were false, defamatory and “extremely salacious”.

Biden’s remarks had been spread widely on social media and reported by media outlets around the world, causing Trump “to suffer overwhelming financial and reputational harm”, Brito wrote.

Biden made the Epstein comments during a sprawling interview in which he lashed out at “elites” and others in the Democratic Party that he said undermined his father ahead of last year’s presidential election campaign.

“Epstein introduced Melania to Trump. The connections are, like, so wide and deep,” Biden said in one of the comments Trump disputes.

Biden attributed the claim to author Michael Wolff, whom Trump disparaged in June as a “third-rate reporter”. He has accused Wolff of making up stories to sell books.

Melania’s threats echo a favoured strategy of her husband, who has aggressively used litigation to go after critics. Public figures like the Trumps face a high bar to succeed in a defamation lawsuit.

The president and first lady have long said they were introduced by Paolo Zampolli, a modelling agent, at a New York Fashion Week party in 1998.

The legal letter is dated August 6 and was first reported on Wednesday by Fox News Digital.

Abbe Lowell, a lawyer who has represented Biden in his criminal cases and to whom Brito’s letter is addressed, did not immediately respond to a request for comment.

-AAP