South Korean President Moon Jae-in's top security adviser has voiced uncertainty over North Korea's willingness to give up its nuclear weapons, saying it ultimately depends on whether the United States offers incentives.

"(North Korean leader Kim Jong Un) did really have willingness to denuclearize when I met him at Panmunjeom in April of 2018 and in Pyongyang in September of the same year. But now? I cannot be sure," Moon Chung-in told reporters at a briefing Friday.

"Whether North Korea gives up on nuclear weapons or not depends on what kind of incentives the United States offers," he added.