The sister of North Korean leader Kim Jong Un has issued a warning to the United States and South Korea ahead of the joint military drills, which the two countries are scheduled to kick off next week.

Kim Yo Jong released a statement through the state-run Korean Central News Agency on Tuesday.

She said North Korea always keeps an eye on the activities carried out by the US and South Korean militaries. The two countries will start engaging in large-scale military drills on March 13.

Kim said the Pacific does not belong to the United States or Japan. She warned that any military response to North Korea's strategic weapons tests will be regarded as a "clear declaration of war."

She added that the North is "always on standby to take appropriate, quick and overwhelming action at any time" according to the country's judgment.

Kim had warned in a statement last month that North Korea could use the Pacific as a "firing range" in response to US actions.