North Korea is preparing to blow up roads that cross the heavily militarized border with South Korea, Seoul said.

North Korean soldiers have been spotted planting explosives in the streets, South Korea’s military spokesman said, with preparations for detonation as early as Monday.

“They have set up screens on the street and are working behind those screens, preparing to blow up the streets,” Lee Sung-jun, a spokesman for South Korea’s general staff, told a briefing.

The destruction of the roads would be in line with Kim Jong Un’s attempt to cut ties with South Korea and formally establish it as the North’s main enemy.

Pyongyang’s decision came after the North accused the South of flying drones over its capital three times this month to drop propaganda leaflets.

The country’s military warned of “terrible destruction” and a “declaration of war” if drones were detected in its airspace again, and claimed it had placed artillery units on the border “ready to open fire.”

According to experts, it is highly unlikely that the North will launch full-scale, pre-emptive strikes, as its military falls far short of the combined forces of the US and South Korea.