The judge presiding over Donald Trump's criminal trial in New York found the former US president in contempt of court on Monday and warned him that more violations could lead to jail time.

Justice Juan Merchan fined Trump $1,000 (€927) for breaching a gag order that prohibits him from making public incendiary comments about jurors, witnesses and others involved in the case.

It is the second time since his trial started last month that Trump has been sanctioned for contempt of court. He was slapped with a $9,000 fine last week — $1,000 for each of the nine violations.

Judge says violations amount to 'attack' on the law

Merchan said Trump's "continued, wilful" violations of the gag order amounted to a "direct attack on the rule of law," and that he was considering jailing the former president as a result.

"As much as I do not want to impose a jail sanction ... I want you to understand I will," Merchan told Trump.

"At the end of the day I have a job to do and part of that job is to maintain the dignity of the justice system," the judge said.

Merchan's ruling came at the start of the third week of testimony in Trump's hush money trial.

Why is Donald Trump in court?

The 77-year-old is accused of falsifying business records to cover up payments made to avoid potentially damaging publicity in the leadup to the 2016 presidential election.  

Prosecutors allege Trump reimbursed his then-lawyer Michael Cohen for a $130,000 payment to adult film actor Stormy Daniels. The money was allegedly to keep her from going public about her claims of a 2006 sexual encounter with the mogul.

Prosecutors allege those transactions were falsely logged in company records as legal expenses.

Trump denies a sexual encounter with Daniels took place.

He has pleaded not guilty, and his lawyers argue the payments were in fact legal expenses, not part of a cover-up.

Besides the case in New York, Trump has also been indicted in Washington and Georgia on charges of conspiring to overturn the results of the 2020 election. He is also facing charges for illegally storing classified documents at his home in Florida after leaving the White House.

nm/ab (Reuters, AP)