The military is closely monitoring North Korea but no unusual signs have been detected so far, the Joint Chiefs of Staff (JCS) said Monday, after Pyongyang warned of "crisis beyond control" and "corresponding action" in a series of statements slamming Seoul and Washington.

On Sunday, the North denounced US President Joe Biden for making the "big blunder" of calling its nuclear program a serious threat and criticized Seoul for failing to stop defectors from flying anti-Pyongyang leaflets.

Kim Yo-jong, sister of North Korean leader Kim Jong-un, said the country will consider the leafleting campaign as a "serious provocation" and look into "corresponding action." She did not elaborate what that could be.

"There were no unusual signs as of now," JCS spokesman Col. Kim Jun-rak said during a regular press briefing. "Our military is closely monitoring related activities and is maintaining a firm readiness posture." (Yonhap)