• A recording of former President Donald Trump shows him acknowledging a document he kept after leaving the White House was classified, NBC News reported.
• The recording was obtained by the special counsel's office leading a criminal investigation into the classified documents and other presidential records that were stored in Trump's Mar-a-Lago home in Florida after he left the White House.
• Trump's remarks in that audio indicate the document was related to Iran.

Follow our live coverage of Donald Trump's indictment in the classified documents case.

A recording of former President Donald Trump shows him acknowledging a document he kept after leaving the White House was classified, NBC News reported Thursday, citing a source directly familiar with the matter.

Trump's remarks on that tape, recorded in 2021, indicate the document was related to Iran, NBC reported.

The recording was obtained by the special counsel's office leading a criminal investigation into the classified documents and other presidential records that were stored in Trump's Mar-a-Lago home in Florida after he left the White House in January 2021. By law, such records must be turned over to the National Archives and Records Administration.

The recording was played during grand jury testimony, the source told NBC. The comments came more than a year before the FBI raided Trump's Florida home to search for the documents.

Trump has denied wrongdoing. He has publicly claimed he had declassified the records that made their way to Mar-a-Lago, including the materials seized in the raid of the property last summer.

CNN first reported Wednesday that federal prosecutors had acquired audio of Trump acknowledging he had held onto a classified document about a possible attack on Iran. The recording was taken at a July 2021 meeting at Trump's golf club in Bedminster, New Jersey, which included the former president's aides and two people working on an autobiography of former White House chief of staff Mark Meadows, CNN reported.

A spokesman for Trump said of CNN's report, "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."

"The DOJ's continued interference in the presidential election is shameful and this meritless investigation should cease wasting the American taxpayer's money on Democrat political objectives," the spokesman added.

The Trump campaign did not immediately respond to a request for additional comment on NBC's reporting. Trump, in a social media post later Thursday, claimed without evidence that the reporting about the special counsel probe was the result of a leak by the Department of Justice.

The investigation into the documents is one of two Trump-related criminal probes being led by special counsel Jack Smith. Attorney General Merrick Garland appointed Smith in November to act independently from the Justice Department, following Trump's announcement he was running for president again in 2024.

Trump, who is currently the frontrunner for the Republican presidential nomination, faces numerous other legal threats. He has pleaded not guilty in a Manhattan prosecution accusing him of falsifying business records related to hush money payments made to two women who allege they had affairs with Trump.

Trump is also embroiled in a Fulton County prosecutor's investigation of potential criminal interference in Georgia's 2020 election.