Columbus: Former US Defence Secretary Leon Panetta said President Donald Trump's summit with North Korea leader Kim Jong-un in June about the country's nuclear threat was "doomed to failure" because of a lack of preparation beforehand.

"I'm very worried about the situation because frankly, I think we have a failed summit on our hands right now," Panetta said on ABC's This Week on Sunday.

Former Defence Secretary Leon Panetta Credit:AP

Trump last month called off a planned trip to North Korea by Secretary of State Michael Pompeo after concluding there hasn't been enough progress in talks aimed at denuclearising the Korean Peninsula. In an August 30 interview with Bloomberg News, the president said he can be patient with the North Korean leader, who's yet to take appreciable steps to give up his country's nuclear weapons after Trump declared the issue solved following the summit.

Panetta, who served as defence secretary and CIA director under Democratic President Barack Obama, said the summit "was all about show, it was about shaking hands, exchanging words."