Donald Trump acknowledged in 2019 that letters he wrote to Kim Jong-un and later took with him upon leaving the White House were secret, according to recordings of an interview he gave to journalist Bob Woodward that call into question the credibility of one of Trump’s main defenses in the investigation into his unauthorized retention of government files.

In December of that year, Trump shared with Woodward the letters that Kim had written to him, saying, “Nobody else has them, but I want you to treat them with respect … and don’t say I gave them to you, OK?” according to recordings obtained by CNN and the Washington Post on Tuesday.

When, in a phone call the following month, Woodward asked to see what Trump had written to the North Korean leader, the president replied: “Oh, those are so top secret.”

The comments contradict Trump’s claim that he took no government secrets with him upon leaving the White House in January 2021. In reality, the National Archives, which is tasked with preserving the records of former presidents, spent much of 2021 trying to get the Kim letters back from Trump, only succeeding earlier this year.

The statements, included in The Trump Tapes: Bob Woodward’s Twenty Interviews With President Trump set for release on Tuesday, also raise questions about the credibility of his defense to allegations that he illegally kept government secrets at his south Florida resort, Mar-a-Lago.

The FBI searched Mar-a-Lago in August and carted away reams of documents, sparking a court battle after the former president claimed some of the papers were protected by executive or attorney-client privilege.

The letters to Kim, written by Trump as part of his administration’s attempt to defuse nuclear tensions with North Korea, show his apparent admiration for the leader of one of the world’s most repressive regimes. The two men exchanged birthday greetings and “best wishes” for friends and family, according to English translations of the letters that the Post reported are included in a written transcript of the audiobooks.

During his visits to the White House, Trump asked Woodward about the documents, and if he had made “a Photostat of them or something”. Woodward replied that he had dictated them into his recorder.

In an interview with the Washington Post, Woodward, an associate editor at the paper who is best known for his work uncovering the Watergate scandal, said Trump allowed him to handle the documents in a West Wing office as an aide watched. The documents contained no obvious classification markings, Woodward said.

In the audiobook, Woodward described “the casual, dangerous way that Trump treats the most classified programs and information, as we’ve seen now in 2022 in Mar-a-Lago, where he had 184 classified documents, including 25 marked ‘top secret’”.

He was talking specifically about Trump’s comment that he “built a weapons system that nobody’s ever had in this country before. We have stuff that you haven’t even seen or heard about.”

Referring to Vladimir Putin and Chinese president Xi Jinping, Trump remarked to the journalist: “We have stuff that Putin and Xi have never heard about before.”