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

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

Special counsel Jack Smith, who is leading the Justice Department investigation into Trump, has focused on the meeting 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.

Prosecutors have asked witnesses about the recording and the document before a federal grand jury. The episode has generated enough interest for investigators to have questioned Gen. Mark Milley, one of the highest-ranking Trump-era national security officials, about the incident.

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.

Meadows' autobiography includes an account of what appears to be the same meeting, during which Trump "recalls a four-page report typed up by (Trump's former chairman of the Joint Chiefs of Staff) Mark Milley himself. 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."

The document Trump references was not produced by Milley, CNN was told.

Investigators have questioned Milley about the episode in recent months, making him one of the highest-ranking national security officials from Trump's administration to meet with the special counsel's team. Milley's spokesman Dave Butler declined to comment to CNN.

The revelation that the former president and commander-in-chief has been captured on tape discussing a classified document could raise his legal exposure as he continues his third bid for the White House. Trump has denied any wrongdoing.

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

"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.

When asked at a CNN town hall this month if he showed classified documents he kept after the presidency to anyone, Trump answered: "Not really. I would have the right to. By the way, they were declassified after."

A lawyer for Meadows declined to comment. A lawyer for Martin declined to comment.

Smith's investigation has shown signs of nearing its end, though it hasn't yet resulted in any criminal charges. A spokesman for the special counsel's office declined to comment for this story.

Trump was outraged at New Yorker story on Milley and Iran

The recording that's now in the hands of prosecutors shows they are not only looking at Trump's actions regarding classified documents recovered from his Mar-a-Lago resort in Florida, but also at what happened at Bedminster a year earlier.

The meeting in which Trump discussed the Iran document with others happened shortly after The New Yorker published a story by Susan Glasser detailing how, in the final days of Trump's presidency, Milley instructed the Joint Chiefs to ensure Trump issued no illegal orders and that he be informed if there was any concern. The story infuriated Trump.

Glasser reported that in the months following the election, Milley repeatedly argued against striking Iran and was concerned Trump "might set in motion a full-scale conflict that was not justified." Milley and others talked Trump out of taking such a drastic action, according to the New Yorker story.

On the recording and in response to the story, Trump brings up the document, which he says came from Milley. Trump told those in the room that if he could show it to people, it would undermine what Milley was saying, the sources said. One source says Trump refers to the document as if it is in front of him.

Several sources say the recording captures the sound of paper rustling, as if Trump was waving the document around, though is not clear if it was the actual Iran document. There's also laughter in the room that's captured on the recording.

The US military has contingency plans and courses of action that apply to countries and situations around the globe.

The meeting took place well before Trump's team shipped 15 boxes of presidential records and classified documents back to the National Archives and Records Administration in January 2022 after months of back-and-forth between his team and the records agency.

The Justice Department later obtained additional documents with classified markings from Trump, seizing more than 100 during a search of Mar-a-Lago last August. Trump's legal team hired people to search other Trump properties, including Bedminster, late last year.

Investigators from the special counsel's office also have asked in their document handling and obstruction investigation about other scenarios in which Trump may have shown national security documents, such as maps, to others, sources say. They've also asked several witnesses to share details about Trump's anger toward Milley.

During the summer of 2021, sources say multiple people were making recordings of Trump as he held conversations with journalists and biographers.

Trump's different explanations on the declassified documents

Trump and his attorneys have given several different, often conflicting, explanations for why Trump didn't intentionally retain classified materials in violation of federal law. 

Initially, Trump allies argued he had a "standing declassification order" so that documents removed from the Oval Office were immediately declassified.  A few weeks later, Trump told Fox News that he could declassify things "just by thinking about it."

Earlier this year, Trump's legal team told Congress that classified material was inadvertently packed up at the end of the administration. Most recently, Trump told CNN at a town hall that materials were "automatically declassified" when he took them.

However, there's no indication Trump followed the legally mandated declassification process, and his attorneys have avoided saying so far in court whether Trump declassified records he kept.

This story has been updated with a response from former President Trump's campaign.