North Korea is preparing to blow up roads crossing its heavily militarized border with South Korea, Seoul said.

Troops of North Korea were seen working on the roads, the South’s military spokesman said, with preparations to detonate as early as Monday.

“They have installed screens on the roads and are working behind those screens as they prepare to blow up the roads,” Lee Sung Joon, spokesman for South Korea’s Joint Chiefs of Staff, told a briefing.

Destroying the roads would be in line with Kim Jong Un’s push to sever ties with South Korea and formally cement it as the North’s main enemy.

It comes after the North accused South launching drones over the capital three times this month to distribute propaganda leaflets.

The country’s military warned of a “terrible disaster” if the drones were re-located and said it has put eight-armed artillery units on the border “on standby to open fire.”

According to experts, the North is highly unlikely to launch large-scale, pre-emptive strikes as its military is outnumbered by the combined US and South Korean forces.

South Korea has refused to confirm whether it has sent drones, but warned it would punish North Korea if the safety of its citizens is compromised.

Officials in the South say the North has added anti-tank barriers, planted mines and fortified roads on its side of the border since earlier this year, in a likely effort to boost security on the front lines and prevent soldiers and civilians from defecting .

Read more from Sky News:
A look inside North Korea’s secret nuclear weapons program
China is conducting major military exercises around Taiwan
Ukraine claims Russia has killed nine drone operators

Tensions between the two are at their highest point in years – with North Korea continuing a series of weapons tests and South Korea expanding military exercises alongside the US.

In January, Kim Jong Un ordered the revision of North Korea’s constitution to remove the goal of peaceful Korean unification and formally designate South Korea as the country’s “immutable principal enemy.”

This was seen as a break with his predecessor’s long-term goal of achieving a unified Korea on the North’s terms.