Former US president Donald Trump said he expects to be arrested on Tuesday in connection with a case brought by the Manhattan district attorney's office.
On his social media platform Truth Social on Saturday, he said that “illegal leaks” from the Manhattan DA’s office indicate that he will be detained.
Mr Trump did not provide any evidence or details of how he knew about the expected arrest, but senior Republicans have supported him.
Even as a Trump lawyer and representative said there had been no communication from prosecutors, the former president rallied his base.
The Manhattan district attorney's office, which has been investigating a $130,000 payment to adult film star Stormy Daniels, declined to comment.
No US president — while in office or afterward — has faced criminal charges.
Mr Trump repeated his false claims of a stolen 2020 presidential election and urged his followers to “protest, take our nation back”.
Similar language was used in his message preceding the riot at the US Capitol on January 6, 2021.
Law enforcement officials in New York have been making security preparations for the possibility of the indictment of Mr Trump.
The grand jury's work in the case has been kept a secret, including any potential vote on whether to indict the former president.
The grand jury has been hearing from witnesses, including former Trump lawyer Michael Cohen, who has said he arranged payments totalling $280,000 to two women to silence them about sexual encounters they said they had with Mr Trump a decade earlier.
Mr Trump denies the encounters occurred and has cast the investigation as a “witch hunt” by a Democratic prosecutor wanting to sabotage his 2024 presidential campaign.
Within hours of the post, the Trump campaign sent out fund-raising solicitations to his supporters, while influential Republicans rallied to his side.
“The idea of indicting a former president of the US is deeply troubling to me as it is to tens of millions of Americans,” said former vice president Mike Pence.
House Speaker Kevin McCarthy said a possible indictment would be “an outrageous abuse of power by a radical DA who lets violent criminals walk as he pursues political vengeance” against Mr Trump.
Senator Lindsey Graham, a long-time Trump ally, said: “They’re doing this because they’re afraid of Donald Trump.”
Meanwhile, Nancy Pelosi, who was the Democratic House speaker when Mr Trump was impeached for inciting the January 6, 2021 riot, called his announcement “reckless”, saying it would “foment unrest among his supporters”.
Mr Trump is facing several criminal investigations.
In Georgia, a prosecutor is investigating efforts to overturn his 2020 election loss. The grand jury in that case has recommended multiple indictments, the forewoman has said.
Mr Trump is also the subject of a federal probe into his handling of classified documents and his possible involvement in the January 6 riot.
So far, no charges have been brought.
Even if he is indicted, any trial of the former US president would still be more than a year away, according to legal experts.
The average criminal case in New York takes more than a year to move from indictment to trial, said Karen Friedman Agnifilo, former Manhattan chief assistant district attorney, and Trump's case is far from typical.
That raises the possibility of Trump having to stand trial in the middle of the 2024 presidential campaign, or even after Election Day, though putting a president-elect or president on trial for state charges would enter uncharted legal waters. If elected, he would not hold the power to pardon himself of state charges.
"This is so unprecedented that it's hard for me to say," Ms Agnifilo said when asked whether a judge would put Trump on trial close to the election. "I think it's tricky."