The powerful sister of the North Korean leader Kim Jong-un warned Monday that it would be "delusional" for the United States to believe that Pyongyang's disarmament was possible.

Kim Yo-jong criticized Washington's policies of strengthening its extended deterrence and military alliance with South Korea, stating that such actions would only make it difficult for Pyongyang to engage in dialogue, according to the North's official Korean Central News Agency.

"The US is being delusional if it believes that it could halt our advancement and further achieve irreversible disarmament by temporarily halting joint military drills, suspending the deployment of strategic assets or reversibly easing sanctions etc," Kim said.

Kim also rejected US calls for unconditional talks, dismissing them as a ploy to hinder North Korea's progress.

"We stand ready to firmly respond to any actions that could infringe upon our sovereignty and harm the stability of our people," Kim said, adding that its recent firing of an intercontinental ballistic missile was just the beginning.

Kim has made several remarks in recent days, including her condemnation of the United Nations Security Council for convening a meeting to discuss the ICBM firing.