Washington DC - Donald Trump's federal gag order was mostly upheld by a US federal appeals court on Friday. The gag was imposed on the former president in his election interference case.

"We do not allow such an order lightly," said Judge Patricia Millett, who wrote the unanimous opinion issued by a three-judge panel of the US Court of Appeals for the DC Circuit.

"Mr. Trump is a former President and current candidate for the presidency, and there is a strong public interest in what he has to say," Millett said.

"But Mr. Trump is also an indicted criminal defendant, and he must stand trial in a courtroom under the same procedures that govern all other criminal defendants."

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The appeals court slightly narrowed the gag order issued by the district court judge who will preside over Trump's trial for allegedly conspiring to overturn the 2020 election won by Democrat Joe Biden.

Judge Tanya Chutkan had barred Trump, the frontrunner for the 2024 Republican presidential nomination, from publicly attacking Jack Smith, the special counsel who brought the historic case against him, other prosecutors, court staff, or potential witnesses ahead of his March trial.

The appeals court removed the gag order on Trump from making comments about Smith but barred him from publicly attacking potential witnesses, other prosecutors, court staff, or their family members.

"Mr. Trump is free to make statements criticizing the current administration, the Department of Justice, and the Special Counsel, as well as statements that this prosecution is politically motivated or that he is innocent of the charges against him," Millett said.

Trump has repeatedly called Smith, the special counsel, "deranged," attacked his colleagues as "thugs," and publicly accused Judge Chutkan of being biased against him.

Arguing against the gag order, Trump's lawyers said it was unconstitutional and runs up against First Amendment protections guaranteeing free speech.

Trump is also the target of another gag order in his current New York civil fraud trial after a flood of online abuse.

Judge Arthur Engoron slapped the gag order on Trump on October 3 after he insulted the judge's principal law clerk in a post on his Truth Social platform.

Trump's attorneys appealed the order claiming it violated his right to free speech but an appeals court reimposed the restrictions.

Engoron has fined the 77-year-old Trump a total of $15,000 for two violations of the gag order.

Trump and his two eldest sons are accused of inflating the value of their real estate assets to receive more favorable bank loans and insurance terms.

Trump additionally faces federal charges for alleged mishandling of top-secret documents after he left the White House, and has been indicted for racketeering in Georgia on accusations that he tried to overturn the 2020 election results in the southern state.