Seoul, South Korea (CNN) A senior North Korean official has called US President Donald Trump a "heedless and erratic old man," the latest insult in an escalating war of words between the two countries.

Kim Yong Chol, Chairman of the Korea Asia-Pacific Peace Committee, made the comment about Trump on Monday in a statement reported by the state-run Korean Central News Agency (KCNA).

It comes a day after Trump warned that the North Korean leader Kim Jong Un could "void" their "special relationship" following reports that the hermit nation conducted an "important" test at a missile site.

On Monday, North Korean officials hit back at Trump. Ri Su Yong, the Vice-Chairman of the Central Committee of the Workers' Party of Korea, warned the President to "think twice if he does not want to see bigger catastrophic consequences."

According to a statement from KCNA, Ri said that Trump appeared "very anxious" to know what North Korea was thinking, and that Trump's recent remarks were a sign "that he feels fear inside."

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