US media have uncovered an audio clip in which former US President Donald Trump appears to admit to keeping a secret document after leaving the White House.

The former President is heard stating, "This is highly confidential," as he leafs through some files on the tape.

The two-minute footage was initially released by CNN, which said it was taken from an interview Trump conducted with authors of his former chief of staff Mark Meadows' biography in July 2021.

Additionally, Trump added, "These are the papers" in reference to a document he calls "highly confidential".

It seems to be an audio tape that federal prosecutors used as evidence when charging the former President.

In one case in July 2021 at his golf club in New Jersey, the prosecution claims he twice showed unqualified individuals, including a writer and two staff employees, secret documents.

Early this month, an indictment made public said former US President Donald Trump is accused of committing 37 felony offenses, including conspiracy to obstruct justice and deliberate retention of national security material.

Trump is accused of withholding a document during a federal investigation, in addition to one count of conspiracy to obstruct justice, 31 counts of intentional retention of national security information, two distinct counts of making false statements, and other connected offenses.

According to the indictment, he could get a term of up to 20 years in jail for a number of crimes.

Trump has lately attacked prosecutors for not pursuing Joe Biden, the current US President, for his alleged improper handling of secret documents in the same manner. Biden has denied the claims of misconduct.

The former US President has repeatedly denied wrongdoing in the case, but he has openly acknowledged taking and storing the documents, undermining his lawyers' suggestion that he took the documents unintentionally.

In the conversation, which CNN and the Washington Post both published on Monday, Trump can be heard detailing a paper that he claims discusses the possibility of striking Iran.

At the beginning of the video, Trump says,  "He said that I wanted to attack Iran. Isn't it amazing?".

"I have a big pile of papers, this thing just came up. Look," he says.

"See as president I could have declassified it," he says. "Now I can't, you know, but this is still a secret."

In a recent interview for Fox News, Trump refuted claims that he gave access to confidential data to others without authorization. 

"There was no document. That was a massive amount of papers and everything else talking about Iran and other things," Trump said. 

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