South Korea said Monday it has detected signs that North Korea is preparing to destroy the northern parts of inter-Korean roads no longer in use, as the rivals are embroiled in soaring tensions over North Korea’s claim that South Korea flew drones over its territory.

Destroying the roads would be in line with leader Kim Jong Un’s push to cut off ties with South Korea, formally cement it as his country’s principal enemy and abandon the North’s decades-long objective to seek a peaceful Korean unification.

In a highly derisive rhetoric, Kim’s sister and senior official, Kim Yo Jong, called the South Korean military “dregs” and “mongrels tamed by Yankees.” She said Monday that “the master of those dogs,” an apparent reference to the U.S., must be held accountable for the alleged drone flights as well. South Korea and the U.S. had no immediate responses.

Earlier Monday, South Korea’s military said that it was observing various activities in North Korea that appeared to be preparations for demolishing the roads, such as installing screens.

“They have installed screens on the roads and are working behind those screens, preparing to blow up the roads,” Lee Sung Joon, spokesperson of South Korea’s Joint Chiefs of Staff, told a briefing. He said the demolitions could be carried out as early as Monday.

Lee said that the South Korean military believes that North Korea may carry out other provocations like a space rocket launch, which the U.N. views as a disguised test of long-range missile technology.

It’s not clear how much parts of the roads North Korea would destroy.

Click to play video: 'North Korea resumes sending trash-filled balloons to South Korea'

During the previous era of inter-Korean detente in the 2000s, the two Koreas reconnected two road routes and two rail tracks across their heavily fortified border. But their operations later were suspended one by one as the Koreas wrangled over North Korea’s nuclear program and other issues.

Last week, North Korea said it would permanently block its border with South Korea and build front-line defense structures to cope with “confrontational hysteria” by South Korean and U.S. forces. South Korean officials said North Korea had already been adding anti-tank barriers and laying mines along the border since earlier this year. They said North Korea has also planted mines and removed lamps along its sections of the inter-Korean roads and taken out ties on the northern side of the railways.

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North Korea has accused South Korea of launching drones to drop propaganda leaflets over Pyongyang three times this month and threatened to respond with force if it happened again. South Korea has refused to confirm whether it sent drones but warned it would sternly punish North Korea if the safety of its citizens is threatened.

In a statement Sunday, the North’s Defense Ministry said that the military had ordered artillery and other army units near the border with South Korea to “get fully ready to open fire.” The ministry said that the entire South Korean territory “might turn into piles of ashes” following the North’s powerful attack.

Click to play video: 'North Korea says underwater nuclear attack drone tested in response to U.S.-led joint naval drills'

North Korea often releases warlike rhetoric when animosities with its rivals increase. Experts say it’s highly unlikely for North Korea to launch full-scale, preemptive attacks as it military is outmatched by the combined U.S. and South Korean forces.

Koo Byoungsam, a spokesperson of South Korea’s Unification Ministry, said Monday that North Korea’s accusation over drone flights was likely aimed at creating tensions to reinforce its internal unity while stoking instability in South Korea. Koo said North Korea cannot win what it wants from South Korea with threats and provocations.

Some observers say anti-Pyongyang activists in South Korea might have sent drones this month, but North Korea argues the South Korean government cannot escape responsibility.

In 2022, South Korea sent surveillance drones across the border into North Korea after it accused North Korea of flying drones into South Korea for the first time in five years.

Tensions on the Korean Peninsula are at their highest point in years, with North Korea continuing a run of provocative missile tests and South Korea and the U.S. expanding their military drills. Observers say North Korea could perform major weapons tests ahead of next month’s U.S. presidential election to increase its leverage in future diplomacy with the Americans.

In January, Kim Jong Un ordered the revision of North Korea’s constitution to eliminate the goal of a peaceful Korean unification, formally designate South Korea as the country’s “invariable principal enemy” and define the North’s sovereign, territorial sphere.

Kim’s order stunned many North Korea watchers because it was seen as breaking away with his predecessors’ long-cherished dreams of peacefully achieving a unified Korea on the North’s terms. Experts say Kim likely aims to diminish South Korea’s voice in the regional nuclear standoff and seek direct dealings with the U.S. They say Kim also likely hopes to diminish South Korean cultural influence and bolster his rule at home.