Former US President Donald Trump said he expects to be "arrested" on Tuesday over hush money allegedly paid to a porn star before the 2016 election, calling on his supporters to protest.

Citing a "leak" from the Manhattan district attorney's office, Trump wrote on his Truth Social platform this morning: "Leading Republican candidate & former President of the United States of America will be arrested on Tuesday of next week. Protest, take our nation back!"

The investigation centres on USD 130,000 paid weeks before the 2016 polls to stop Stormy Daniels, whose real name is Stephanie Clifford, from going public about an affair she says she had with Trump years earlier.

Prosecutors are weighing whether to charge Trump in the case, and speculation is rife that an indictment is likely.

If the Manhattan district attorney were to indict Trump, the 76-year-old would become the first former president to be charged with a crime. That would also upend his bid to win the Republican nomination for the 2024 presidential election.

Trump's lawyer told CNBC on Friday evening that his client would surrender to face criminal charges if he was indicted by a Manhattan grand jury.

Trump has denied having an affair with Daniels and has dismissed the investigation as politically motivated.

In his post, written in capital letters, Trump referred to "illegal leaks from a corrupt & highly political Manhattan district attorneys office" and said the investigation was "based on an old & fully debunked (by numerous other prosecutors!) fairytale."

Daniels met with prosecutors on Wednesday and "agreed to make herself available as a witness, or for further inquiry if needed," according to her lawyer Charles Brewster.

Earlier this month, Trump was given the opportunity to testify by District Attorney Alvin Bragg's team but declined to avoid potentially incriminating himself. Experts say the invitation is a sign that he will almost certainly be charged.