SEOUL, South Korea (AFP) — North Korea blew up sections of the deeply symbolic roads connecting it to the South on Tuesday, Seoul’s military said, adding it had conducted a “counter-fire” operation in response.

Pyongyang’s military last week vowed to permanently seal its southern border after spending months laying mines and building anti-tank barriers in the wake of leader Kim Jong Un declaring the South his country’s “principal enemy.”

The North also accused Seoul of using drones to drop anti-regime propaganda leaflets on the capital Pyongyang, with Kim convening a security meeting to direct a plan of “immediate military action” in response, state media reported Tuesday.

“North Korea has detonated parts of the Gyeongui and Donghae roads north of the Military Demarcation Line (MDL),” the Joint Chiefs of Staff said Tuesday, referring to inter-Korean infrastructure that once connected the two countries.

“There has been no damage to our military, and our forces conducted counter-fire in areas south of the MDL,” it added.

The roads have long been shuttered, but destroying them sends a clear message that Kim is not prepared to negotiate with the South, experts said.

“This is a practical military measure related to the hostile dual-state system that North Korea has frequently mentioned,” Yang Moo-jin, president of the University of North Korean Studies in Seoul, told Agence France-Presse.

The North may also be looking to erect more physical barriers along the border, Yang said, adding that the road detonations could be “preparatory work.”