A former senior adviser to multiple American presidents, Harald Malmgren, claims he was briefed on “otherworld technologies” by a top CIA official in the 1960s.

Mr. Malmgren, who served under Presidents Kennedy, Johnson, Nixon, and Ford, made the assertion regarding an alleged conversation with a CIA officer, Richard Bissell, in a post on social media platform X this week.

“Sixty-plus years ago I was provided highest level classifications to lead DOD work on nuclear weapons and antimissile defense,” Mr. Malmgren wrote, referring to the Department of Defense. “Informally briefed on ‘otherworld technologies’ by CIA’s Richard Bissell (who had been in charge of Skunkworks, Area 51, Los Alamos, etc.) but sworn to secrecy.”

“What I learned was sketchy, slightly illuminated by Bissell as he felt I needed a heads up in case the subject ever came up in my meetings with presidents or others,” he wrote. “I swore secrecy to him, not under any law.”

As a reason for speaking up now, Mr. Malmbren wrote, “I simply thought time has come for the rest of humanity to start thinking about what it means for understanding of the world in which we live.”

The claim comes amid the release of a book by a former employee of the Pentagon’s secret UFO program, Luis Elizondo. In it, Mr. Elizondo expresses his belief that the American government possesses advanced technology created by non-human intelligence.

Mr. Malmgren said he’s not a source for the book. “I am not seeking public confirmation status — just telling my personal story,” he wrote. “Confirmations will be up to others directly involved, in coming months,” adding: “I never directly worked on UAPs, nor indirectly used such research in my own work” and therefore “cannot be treated as a source of confirmation of UAP info.”