The South Korean military has reportedly told units to strengthen surveillance and vigilance against North Korea and enhance firepower readiness in response to escalating threats from North Korea.

A military source said Monday that the Joint Chiefs of Staff(JCS) issued instructions to heighten readiness. 

The JCS said the military is closely watching the movements of North Korean troops and maintaining its readiness posture, but it refused to elaborate. 

North Korea is escalating its threats against South Korea, saying South Korean drones carrying propaganda leaflets trespassed into Pyongyang three times this month.  

In a statement carried by the North’s state Korean Central News Agency(KCNA) on Saturday, Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, warned South Korea of a "horrible disaster" if its drones are found flying over the North's capital again.

The KCNA reported Sunday that the general staff department of the North Korean army had ordered artillery units near the border with South Korea to get ready to open fire.