Former U.S. National Security Adviser John Bolton has claimed in his upcoming memoir that diplomatic efforts to denuclearize North Korea in 2018 were South Korea's "creation," and neither Washington nor Pyongyang's strategy.

According to CNN on Thursday, Bolton wrote in "The Room Where It Happened," due to be published next week, that the "whole diplomatic fandango" related more to Seoul's unification agenda.

At the first U.S.-North Korea summit in Singapore in June 2018, Bolton said President Donald Trump was "desperate to have the meeting at any price" and that North Korean leader Kim Jong-un had him "hooked" in Singapore.

The New York Times quoted Bolton as saying the decision to meet Kim in Singapore was a "foolish mistake," and Trump's desire to invite Kim to the White House was "a potential disaster of enormous magnitude."

On Twitter, Trump accused Bolton of hampering diplomacy by saying he was considering the "Libyan Model" for North Korea in April 2018, requiring the North to first surrender its nuclear and ballistic missile programs in return for concessions.

Claiming Bolton apologized, Trump said he should have fired him at the time. Bolton left the administration in September last year, after clashing with Trump on multiple policy issues, including North Korea.