North Korea accused its southern counterpart on Friday of repeatedly flying drones into the area surrounding the capital city of Pyongyang in order to drop leaflets criticizing supreme leader Kim Jong Un’s regime.

The South Korean government has not provided comment on the existence or nature of the alleged drones but conveyed preparedness in case of escalation.

South Korean Joint Chiefs of Staff spokesman Lee Sung-joon said the military is “closely monitoring the situation and standing fully ready for the North’s provocations.”

Lee claimed Korean People’s Army officials have “installed screens on the roads and are working behind those screens, preparing to blow up the roads” connecting North Korea and South Korea.

Kim Yo Jong, the supreme leader’s sister and vice department director of the Central Committee of the Workers’ Party of Korea, spoke on Monday against the alleged drone incursions and placed blame for the incident on the United States.

“We clearly know that the military dregs of the ROK are chiefly to blame for the case of drone infiltration into Pyongyang,” Kim Yo Jong said.

She also flexed North Korean nuclear capabilities, warning that “if the sovereignty of a nuclear weapons state was violated by mongrels tamed by Yankees, the master of those dogs should be held accountable for this.”

The destruction of the few roads connecting North Korea to South Korea would be just the latest in a series of pivots against inter-Korean cooperation undertaken by the Kim regime.

Kim Jong Un is overseeing the modification of his nation’s constitution to designate South Korea as its primary enemy, abandoning all pretenses of reunification. The constitutional restructuring was first floated in January.

Military engagements between North Korea and South Korea ended in 1953 with the signing of an armistice, but a lack of a treaty ending the Korean War means the two nations remain in armed conflict on paper.