NEW YORK (AP) — Manhattan prosecutors investigating Donald Trump have convened a new grand jury to hear evidence in a years-old probe into payments made to keep the porn star Stormy Daniels quiet about an alleged sexual encounter with the former president, according to multiple news reports.

The news outlets, citing unnamed sources, reported that witnesses started testifying before the grand jury on Monday, signaling an escalation in what Manhattan District Attorney Alvin Bragg has alluded to as "the next chapter" in his office's Trump investigation.

A spokesperson for Bragg's office declined comment. In a post to his Truth Social platform, Trump blasted Bragg as the "Radical Left Manhattan D.A." and said the new grand jury was "a continuation of the Greatest Witch Hunt of all time."

Grand juries have been convened before in New York to explore the possibility of criminal charges against Trump, but to date none have issued an indictment.

The Manhattan grand jury would be the latest legal threat to Trump as he ramps up his presidential campaign.

A special grand jury in Atlanta has investigated whether Trump and his allies committed any crimes while trying to overturn his 2020 election loss in Georgia. Last month, the House Jan. 6 committee voted to make a criminal referral to the Justice Department for Trump's role in sparking the violent insurrection at the U.S. Capitol. The FBI is also investigating Trump's storage of classified documents.

The hush-money investigation in New York involves payments of $130,000 to Daniels and $150,000 to former Playboy model Karen McDougal to buy their silence in the run-up to Trump's 2016 election victory. Trump has denied having affairs with either woman.

Trump's former personal lawyer and fixer, Michael Cohen, made the payment to Daniels through his own company and said he then was reimbursed by Trump. McDougal's payment was made through the publisher of the supermarket tabloid the National Enquirer, which then squelched her story in a journalistically dubious practice known as "catch-and-kill" to help Trump become president.

The New York Times reported that the National Enquirer's former publisher, David Pecker, was spotted entering the building where the grand jury was meeting on Monday.

Cohen pleaded guilty in 2018 to federal charges that he violated campaign finance law by arranging the payouts. He served about a year in prison before being released to home confinement because of the COVID-19 pandemic. Federal prosecutors said Trump was aware of the payouts, but they declined to charge him with any crime.

Cohen previously told The Associated Press he recently met with Manhattan prosecutors for 2½ hours.

The Trump Organization was convicted last month of tax fraud and fined $1.6 million as punishment for an unrelated scheme in which top executives dodged personal income taxes on lavish job perks.

"Now with the trial having ended, we are now moving on to the next chapter," Bragg told The Associated Press in an interview after the tax fraud trial.

The Trump Organization in a statement suggested that Bragg, a Democrat, was trying to undermine Trump's fledgling 2024 presidential campaign. Reviving the investigation years after federal prosecutors had decided not to bring a case is "simply reprehensible and vindictive," the company said.

Bragg's predecessor as district attorney, Cyrus Vance Jr., also examined the hush money payments before shifting the probe's focus to the Trump Organization's tax and business practices.