Former U.S. National Security Adviser John Bolton said it was "perfectly evident" that the Donald Trump administration's policy approach towards North Korea's denuclearization was a mistake that was doomed to fail.

During a special lecture at Duke University on Monday, Bolton said "there is not a single piece of evidence that the government of North Korea has made a strategic decision to give up the pursuit of nuclear weapons."

On policies towards Iran, Bolton said the Trump administration's sanctions have had a "very significant effect," but added he would like Washington to explicitly push for regime change in the country.

Bolton, whose highly anticipated book about his time in the Trump administration is under review by the White House, declined to answer questions about North Korea, however.

Stating he included in the book things Trump said to him, Bolton expressed hope that his book manuscript will not be “suppressed” and become public someday.