The judge overseeing Donald Trump's criminal trial on Monday said he would hold the former president in contempt of court for a 10th time for violating a gag order, and warned he would consider jailing him for any further violations.

Justice Juan Merchan said the nine fines he had imposed so far did not seem to be deterring Trump from violating the gag order, which prohibits him from making public comments about jurors, witnesses and families of the judge and prosecutors if the statements mean to interfere with the case.

Merchan said he considered jail time “truly the last resort” for many reasons, including the disruption to the trial, the political implications of jailing a leading presidential candidate ahead of an election and the extraordinary security challenges of incarcerating an ex-president with a lifetime Secret Service detail.

But he said Trump’s “continued, willful” violations of the gag order amounted to a “direct attack on the rule of law.”

“I do not want to impose a jail sanction and have done everything I can to avoid doing so. But I will if necessary,” Merchan said from the bench in the absence of the jury.

New York law allows fines of up to US$1,000 or jail time of up to 30 days for violating a court-imposed gag order. (Reuters)