Kim Yo Jong, the powerful sister of North Korea's leader Kim Jong Un. (Photo: Yonhap)

North Korea is convinced it must further perfect a "nuclear war deterrence" as a result, Kim said.

Kim's remarks came amid South Korea’s President Yoon Suk Yeol's six-day state visit to the US for a summit marking 70 years of the US-South Korea alliance. Yoon said that South Korea and the US must unite against threats from North Korea.

The US is committed to providing South Korea with more insight into its nuclear plan to deal with any conflict from North Korea, amid concerns about its growing nuclear program.