Federal prosecutors investigating former President Donald Trump's handling of classified material have a recording of Trump from 2021 discussing a sensitive military document he had kept after leaving the White House, two people briefed on the matter said.

The recording, in which Trump also indicated he knew the document was secret, could undermine his repeated claim that he had already declassified material that remained in his possession after he left office. Prosecutors are scrutinizing whether Trump obstructed efforts by federal officials to retrieve documents he took with him after leaving office and whether he violated laws governing the handling of classified material.

The existence of the recording was reported earlier by CNN.

The tape was made during a meeting Trump held in July 2021 with people helping his former chief of staff, Mark Meadows, write a memoir of his 10 months in the White House, according to the people briefed on the matter. The meeting was held at Trump's club at Bedminster, New Jersey, where he spends summers.

Until now, the focus of the documents investigation has been largely on material Trump kept with him at Mar-a-Lago, his private club and residence in Florida, rather than in New Jersey.

Meadows did not attend the meeting, but at least two of Trump's aides did. One, Margo Martin, routinely taped the interviews he gave for books being written about him that year.

On the recording, Trump began railing about his hand-picked chair of the Joint Chiefs of Staff, Gen. Mark Milley, who was described in media accounts at the time as having guarded against Trump's striking Iran in the final days of the presidency, according to the people briefed on the matter.

Trump then began referencing a document that he had with him, saying that it had been compiled by Milley and was related to attacking Iran, the people briefed on the matter said. Among other comments, he mentioned his classification abilities during the discussion, one person briefed on the matter said. Trump can be heard handling paper on the tape, although it is not clear whether it was the document in question.

The Justice Department obtained the recording in recent months, a potentially key piece in a mountain of evidence that prosecutors have amassed under special counsel Jack Smith since he was appointed in November to oversee the federal investigations into Trump.

Martin was asked about the recording during a grand jury appearance, according to two people briefed on the matter.

Steven Cheung, a spokesperson for Trump, said in a statement that "leaks from radical partisans behind this political persecution are designed to inflame tensions and continue the media's harassment of President Trump and his supporters." He accused prosecutors of interfering with the election through the investigation, which began in early 2022.

Trump has long touted what he claimed was his ability to automatically declassify materials and has even said he could do so with his mind.

His allies have insisted that he had a standing order to declassify material when he took it from the Oval Office to the White House residence, a claim that several former senior administration officials have suggested is nonsense. Members of his legal team have cautioned his aides not to lean too heavily on that argument as a defense in the documents case.

That claim was raised most vocally by Kash Patel, a close adviser to Trump who testified to a grand jury under an immunity deal forced on him by prosecutors.

The recording obtained by the special counsel's office could help prosecutors undercut any argument by Trump that the documents he had taken from the White House upon leaving office were declassified. It could also assist them in making a case that Trump was aware that his abilities to possess — and to show off — classified materials were limited.

Investigators have been asking witnesses about Milley in various interviews for several weeks, although they have generally left unclear what they were looking for.

Investigators have several if not all of the recordings of book interviews that Trump gave, according to two people familiar with the events.

In one interview, Trump said he had taken "nothing of great urgency" when asked if he had anything in his possession.

Trump has equivocated when asked if he ever showed any classified documents to people once he left the White House. At a CNN town hall event in May, he said, "Not really. I would have the right to. By the way, they were declassified after."

Meadows, in his book, appeared to echo Trump's claim about Milley.

"The president recalls a four-page report typed up by Mark Milley himself," the book said. "It contained the general's own plan to attack Iran, deploying massive numbers of troops, something he urged President Trump to do more than once during his presidency. President Trump denied those requests every time."

Yet according to a person familiar with the document in question, the report was not written by Milley and in fact dates to an earlier period in the Trump administration, when Gen. Joseph F. Dunford Jr. was the chair of the Joint Chiefs of Staff and Jim Mattis was the defense secretary.

Milley has been interviewed by investigators about the matter, according to one person briefed on the discussion.

This article originally appeared in The New York Times.