Federal prosecutors have obtained an audio recording of a summer 2021 meeting in which former US President Donald Trump acknowledges he held onto a classified Pentagon document about a potential attack on Iran, multiple sources told CNN on Wednesday.

The recording indicates Trump understood he retained classified material after leaving the White House, according to multiple sources familiar with the investigation.

In the recording, Trump’s comments suggest he would like to share the information but he’s aware of limitations on his ability post-presidency to declassify records, two of the sources said.

CNN has not listened to the recording, but multiple sources described it. One source said the relevant portion on the Iran document is about two minutes long, and another source said the discussion is a small part of a much longer meeting.

Last August, the US government recovered more than 300 documents with classified markings from Trump's Mar-a-Lago home in Florida.

The New York Times reported that the classified documents included material from the CIA, the National Security Agency and the FBI.

A later report indicated that a document describing a foreign government’s military defenses, including its nuclear capabilities, was found by FBI agents during the search of Trump’s home.

A subsequent report said some of the classified documents recovered by the FBI from Mar-a-Lago included highly sensitive intelligence regarding Iran and China.

In November of 2022, US Attorney General Merrick Garland appointed prosecutor Jack Smith as special counsel to oversee investigations into Trump, including the probe of the classified documents.

Smith has focused on the meeting in question as part of the criminal investigation into Trump’s handling of national security secrets. Sources describe the recording as an “important” piece of evidence in a possible case against Trump, who has repeatedly asserted he could retain presidential records and “automatically” declassify documents.

The July 2021 meeting was held at Trump’s golf club in Bedminster, New Jersey, with two people working on the autobiography of Trump’s former chief of staff Mark Meadows as well as aides employed by the former president, including communications specialist Margo Martin. The attendees, sources said, did not have security clearances that would allow them access to classified information. Meadows didn’t attend the meeting, sources said.

A Trump campaign spokesman said “leaks” are meant to “inflame tensions” around Trump.