Former US President Donald Trump appears to acknowledge in a 2021 recording that he had a classified document related to Iran that he did not declassify before leaving office.

In the recording, published by various US media on Monday, Mr Trump is heard speaking to some people, including members of his team, and bragging about the sensitive document.

The audio forms an important piece of evidence for special counsel Jack Smith in the indictment of Mr Trump, accused of risking national security by mishandling classified documents after leaving office.

The Justice Department has also accused Mr Trump of hindering the government’s efforts to retrieve alleged classified documents in his possession.

“See, as president I could have declassified it, now I cannot. Isn’t that interesting? It’s so cool,” Mr Trump said on the recording.

The former president also points out that the document that he attributes to the Department of Defence, refers to Iran.

In the nearly two-minute recording, Mr Trump describes the document as ‘highly confidential’ and ‘secret information’.

“You probably didn’t believe me, but now you believe me. It’s incredible,” he says.

The recording was made on July 21 at Mr Trump’s Golf Club in Bedminster, New Jersey. However, it is the first time the audio has been made public.

The leak, first published by CNN, comes days after the special prosecutor in charge of the case of the classified documents found at Mr Trump’s residence asked to delay the trial until December.

In a court document delivered on Friday, the US government requested the extension, arguing that the case “has to do with classified information, so the defence will need to obtain the required security clearances.”

On Tuesday, the lead judge ordered the jury trial to begin on August 14 in Fort Pierce, some 200 kilometres from Miami.

Mr Trump was charged in the Miami courts with 37 federal criminal offences for mishandling official documents.

Mr Trump has pleaded not guilty. Of the 37 charges, 31 are for knowingly withholding US defence-related documents.

Some of the crimes are punishable by up to 20 years in prison and carry a $250,000 fine.

-EFE