Former US president Joe Biden appeared to discuss sensitive information and describe possessing classified documents in audio recordings released on Monday by the Oversight Project, a conservative activist group.

The heavily redacted transcripts and recordings were made in 2016 and 2017, while Biden was working with a ghostwriter on his 2017 memoir, Promise Me, Dad: A Year of Hope, Hardship, and Purpose. No classified material was ever alleged to have appeared in the book.

Biden, at times, seems to struggle to remember certain details or dates regarding events and topics in the transcripts and recordings, prompting the Oversight Project – as well as some conservative media outlets – to allege that he was “already demonstrating significant cognitive decline” in the years before he ran for president.

In a recording dated October 2016, near the end of Biden’s second term as vice- president under former president Barack Obama, Biden can be heard discussing notes he says he kept from his time in office.

“There was a lot of stuff going on at the same time in foreign policy,” Biden said. “You didn’t want to go into it, but I have extensive notes … over this period of time.”

“Oh, that’s in – oh, you actually have those here,” the writer responds. To which Biden says, “yeah, now, there’s a lot of other notes too”, and goes on to say: “These – this is my – they didn’t even know I had this.”

“Some of this stuff, I’m not, you know, going to – um so I go back, you know what I mean?” Biden continues. “I have stuff on, you know, five – here we go, I mean, it’s like … I have stuff on all the way up to 5/19.”

A representative for Biden didn’t immediately respond to a request for comment from the Guardian on Tuesday about the recordings. But a spokesperson for Biden told CBS News: “President Biden’s conversations for a book a decade ago that discussed his late son are private, and were provided to the Department of Justice on the express condition they stay that way.”

“Reversing course and making them public is just the latest example of this Administration weaponizing the DoJ for political retribution,” they added. “It’s wrong, and while President Biden disagrees with today’s decision, he also respects the courts and the vital role an independent judiciary plays in a healthy democracy.”

Classified materials were also found at President Donald Trump’s Mar-a-Lago club after he left office following his first term. In 2024, a federal judge dismissed the case, ruling that the special counsel who brought the prosecution had been improperly appointed.

The tapes of Biden appear to align with the findings in former special counsel Robert Hur’s 2024 report on his handling of classified documents. That report concluded that Biden had “willfully” kept and shared classified information “after his vice presidency when he was a private citizen” including “classified documents about military and foreign policy in Afghanistan” and handwritten notes about national security and foreign policy “implicating sensitive intelligence sources and methods”.

The report also stated that Biden, during his eight years as vice-president, “regularly wrote notes by hand in notebooks” and that some of those notes “related to classified subjects” and that “some of the notes are themselves classified”.

It also said that Biden “shared information, including some classified information, from those notebooks with his ghostwriter”.

Hur described Biden as a “sympathetic, well-meaning, elderly man with a poor memory”, prompting a furious response from the then president and his officials, and claimed that Biden’s “memory was significantly limited, both during his recorded interviews with the ghostwriter in 2017, and in his interview with our office in 2023”.

But Hur ultimately determined that no criminal charges were warranted, in part because he said it would be hard to convince a jury that “a former president well into his 80s” was guilty of a felony that “requires a mental state of willfulness”.

The Oversight Project, a branch of the Heritage Foundation, sued for the tapes, which had been handed over to the justice department during its investigation into Biden’s handling of the records. House judiciary committee Republicans also sought the tapes. Biden had fought the release, but recently withdrew his legal challenge after a federal appeals court rejected his effort.

In another recording dated 3 November 2016, Biden tells the writer: “And, and then – and then the next thing I have here is – this is classified. It’s all – it goes through the 17th.” The context of this clip is not clear.

In a separate recording dated 16 February 2017, about a month after Biden left office, Biden tells the ghostwriter: “After that diary entry, the next one, between that and the 7th of July” was a “was a long meeting on the Security Council on – and part of it’s classified”.

Later in that recording, Biden says: “So this was – I, early on, in ’09 – I just found all of the classified stuff downstairs. I wrote the President a handwritten 40-page memorandum arguing against deploying additional troops to Iraq – I mean, to Afghanistan – on the grounds that it wouldn’t matter, that the day we left would be like the day before we arrived.”

In a statement on Monday, the Oversight Project said that since 2024, it and the Heritage Foundation “fought tooth and nail to bring these tapes to light”.