Seoul, Aug 10 : Kim Yo-jong, the sister of North Korean leader Kim Jong-un, on Tuesday slammed the US and South Korea over their joint military drills, vowing to build up Pyongyang's nuclear weapons in response. In a statement carried by Pyongyang's official Korean Central News Agency (KCNA), Kim Yo-Jong said: "They (exercises) are the most vivid expression of the US hostile policy, designed to stifle our state by force, and an unwelcoming act of self-destruction for which a dear price should be paid as they threaten the safety of our people and further imperil the situation on the Korean Peninsula. "We will put more spur to further increasing the deterrent of absolute capacity to cope with the ever-growing military threats from the US, i.e. the national defence capabilities and powerful pre-emptive strike for rapidly countering any military actions against us." Besides slamming the drills, she also demanded the withdrawal of the US forces stationed in South Korea, Seoul's Yonhap News Agency reported. "For peace to settle on the peninsula, it is imperative for the US to withdraw its aggression troops and war hardware deployed in South Korea. "As long as the US forces stay in South Korea, the root cause for the periodic aggravation of the situation on the Korean Peninsula will never vanish," she added. North Korea has long denounced Seoul and Washington's military drills as a rehearsal for an invasion of Pyongyang. The allies say that the exercises are defensive in nature. Responding to Kim Yo-Jong's remarks, South Korea said that it will closely monitor North Korea's future actions and brace for any possibilities. But the US declines to "comment on planned or conducted training readiness", Lt. Col. Martin Meiners told Yonhap News Agency. /IANS