North Korea has accused rival South Korea of flying drones to its capital to drop anti-North Korean propaganda leaflets and threatened to respond with force if such flights occur again. South Korea issued a vague denial of the allegation.

North Korea’s Foreign Ministry said in a statement Friday that South Korean drones were detected in the night skies of Pyongyang on Oct. 3 and Wednesday and Thursday this week.

The ministry accused the South of violating North Korea’s “sacred” sovereignty and threatening its security, and described the alleged flights as a “dangerous provocation” that could escalate to an armed conflict and even war.

It said North Korean forces will prepare “all means of attack” capable of destroying the southern side of the border and the South Korean military, and respond without warning if South Korean drones are detected in its territory again.