Former United States President Donald Trump faces charges in relation to a New York investigation into an alleged hush-money payment made to a porn star ahead of the 2016 presidential election.

After weeks of speculation, a New York grand jury voted on Thursday to indict Trump, the New York Times first reported, making him the first former president to face criminal prosecution in US history.

The specific charges are not yet known and the indictment will likely be announced in the coming days, the NYT said.

In a statement released through his 2024 presidential campaign, Trump called the indictment “political persecution and election interference at the highest level in history”.

He said the case was part of a coordinated “witch hunt” against him, adding that he is completely innocent.

The New York investigation centres on a $130,000 payment that Michael Cohen, Trump’s former personal lawyer and fixer, made to porn star Stormy Daniels in the waning days of the former president’s 2016 campaign.

Trump said earlier this month that he expected to be arrested in relation to the case.

He called on his supporters to protest in a fiery social media post that raised concerns about potential violence – especially in light of the January 6, 2021, storming of the US Capitol by a pro-Trump mob.

Reporting from Washington, DC, Al Jazeera’s Mike Hanna said the indictment comes at a surprising time, with the New York grand jury last sitting on Monday.

“But experts point out that what could have happened is that the grand jury … could have agreed on the indictment and then it is up to the foreperson of the jury to sign that indictment at any time that the prosecutor wishes to get it signed,” he said.

This is third world prosecutorial misconduct. It is the opportunistic targeting of a political opponent in a campaign year.

— Eric Trump (@EricTrump) March 30, 2023

“The exact details of what charges will emerge from this [are] also not known at this particular stage,” said Hanna.

He added that Trump would be told when he has to appear in Manhattan court, “where he would be fingerprinted and charges formally laid”, but it also remains unclear when that would happen.

Daniels, whose real name is Stephanie Clifford, said she had an affair with Trump, who is married, and Cohen said he paid her on Trump’s orders.

The former president has denied the affair and said the payment was to protect his reputation from a false accusation, insisting that he did nothing wrong.

Ahead of Thursday’s indictment, several US media outlets had reported that the potential charges relate to the way Trump reimbursed Cohen, with prosecutors alleging he improperly labelled the payments as legal expenses.

If the payment is determined to be a campaign donation, it could also have violated election laws that cap contributions to political candidates at $2,700 per individual and require them to be made public.

Meanwhile, a lawyer for Daniels said the indictment was “no cause for joy”.

“The hard work and conscientiousness of the grand jurors must be respected,” he wrote. “Now let truth and justice prevail.”

Trump’s son, Eric Trump, called the indictment “third world prosecutorial misconduct”.

“It is the opportunistic targeting of a political opponent in a campaign year,” he said.

The indictment of Donald Trump is no cause for joy. The hard work and conscientiousness of the grand jurors must be respected. Now let truth and justice prevail. No one is above the law. #teamstormy

— clark brewster (@cbrew1) March 30, 2023

Trump has already announced plans to seek re-election in 2024, with Al Jazeera’s Hanna noting that an indictment would not preclude him from running.

“Any person who’s been indicted, or in fact sentenced, can still stand for president in the United States in terms of the constitution,” Hanna said.

“Whether or not it galvanises his base … is something that remains to be seen.”

This is a developing story. More updates to follow.