Miami, Florida - Donald Trump faces fresh charges that he attempted to obstruct the investigation into the mishandling of classified documents by conspiring to delete surveillance footage at his Mar-a-Lago property in Florida.

Federal prosecutors unsealed the new indictment targeting the front-runner in the 2024 Republican presidential primary, who is set to go on trial as the election heats up in May of next year.

The new charges came the same day Trump said his lawyers met with Justice Department officials ahead of a separate expected indictment over his alleged efforts to overturn the result of the 2020 election.

The twice-impeached former president was first indicted in the classified documents case last month, accused of endangering national security by holding on to top secret nuclear and defense information after leaving the White House.

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Trump kept the files unsecured at his Mar-a-Lago home in Florida and blocked official efforts to retrieve them, according to the indictment.

Thursday's superseding indictment accuses the former president of acting with his co-defendant in the case, personal aide Waltine "Walt" Nauta, and a new defendant, property manager Carlos de Oliveira, to delete security camera footage at Mar-a-Lago.

The fresh charges add to the existing counts of "willful retention of national defense information" and charges of conspiracy to obstruct justice, making false statements and other offenses to which Trump pleaded not guilty last month.

The new indictment recounts a conversation between de Oliveira and a fourth, unnamed employee in which de Oliveira says "the boss" wants the server deleted.

It also adds an extra count under the Espionage Act related to Trump allegedly retaining a classified document "concerning military activity in a foreign country."

According to the indictment, citing an audio recording of the interaction, Trump in 2021 allegedly told visitors of his New Jersey golf club of the defense document, "'As president I could have declassified it,' and 'Now I can't, you know, but this is still a secret.'"

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On Thursday night, the 77-year-old dismissed the new accusations as "ridiculous" during an interview with Fox News Digital.

"It's election interference at the highest level," he said, blaming his potential campaign opponent President Joe Biden and the Justice Department for "prosecutorial misconduct."

And in a terse statement, his campaign called the special counsel appointed to the case, Jack Smith, "deranged" and said he "knows that they have no case."

A judge last week ordered Trump's trial over the secret documents to begin in May of next year, at the height of what is expected to be a bitter and divisive presidential election campaign.

Earlier Thursday, Trump's lawyers met with Smith and were informed an indictment in the separate January 6 case was looming.

Trump had said his team was not told when any indictment over that case, centered on the 2021 attack on the US Capitol by his supporters, would be issued.

"My attorneys had a productive meeting with the DOJ this morning, explaining in detail that I did nothing wrong, was advised by many lawyers, and that an indictment of me would only further destroy our country," Trump said on social media.

"No indication of notice was given during the meeting – Do not trust the Fake News on anything!"