A New York judge has fined Donald Trump for violating a gag order in his civil fraud trial.

Mr Trump was fined $5,000 (£4,100) by Judge Arthur Engoron on Friday.

The judge said in court that the former president had failed to remove an online post mocking a clerk at the court.

He also threatened Mr Trump with jail time and demanded he take down the "untrue and disparaging" post made about the clerk earlier this month.

Judge Engoron said the post was deleted on social media but remained on his website.

"Incendiary untruths can and have led to serious physical harm," Judge Engoron said in court on Friday.

"I will now allow the defendant to explain why this should not end up with serious sanctions or I could possibly imprison him."

Mr Trump's lawyer, Christopher Kise, apologised on his client's behalf and said it was an "inadvertent" mistake because while the post was deleted from social media, aides forgot to remove it from the campaign website.

Later in the day, Judge Engoron ruled that Mr Trump pay a fine given that "the violation was inadvertent, and given that it is a first time violation".

"Make no mistake: future violations, whether intentional or unintentional, will subject the violator to far more severe sanctions, which may include, but are not limited to, steeper financial penalties, holding Donald Trump in contempt of court, and possibly imprisoning him," Judge Engoron said in his ruling.

Mr Trump and several of his family members are on trial for fraud, falsification of business records, issuing false financial statements and conspiracy.

The non-jury, civil trial is focused on determining damages for the fraud that Judge Engoron has already determined Mr Trump committed by inflating his personal net worth to secure favourable loan agreements.

New York Attorney General Letitia James, who brought the case, is seeking $250m (£205m) in penalties and severe restrictions for Mr Trump's businesses.

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Judge Engoron issued a gag order against Mr Trump on 3 October after he made a post on his social media site Truth Social disparaging the judge's clerk.

In the post, Mr Trump, a Republican, had shared a picture of the clerk alongside Senate Democratic leader Chuck Schumer, claiming she was his "girlfriend".

It was not the first time this week that the judge admonished the former president, who attended several days of the trial.

On Wednesday, Judge Engoron told Mr Trump and others to be quiet during a real estate appraiser's testimony on the witness stand. Mr Trump was reportedly shaking his head and throwing his hands in the air in frustration.

After a request from a lawyer with the New York Attorney General's Office, Judge Engoron asked people to keep their voices down, "particularly if it's meant to influence the testimony".

The same day, a New York court employee was arrested after she shouted out to Mr Trump, "indicating she wanted to assist him", said court officials.

She was escorted out of court, placed on administrative leave and charged with contempt of court.

The New York fraud case is one of several legal battles that the former president faces this year, including both federal and state criminal charges.