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 denied 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.

“The safety lock on our trigger has now been released,” the ministry said. “We will be prepared for everything and will be watching. The criminals should no longer gamble with the lives of their citizens.”

Asked about the North Korean claims during a parliamentary hearing, South Korean Defense Minister Kim Yong-hyun told lawmakers, “We have not done that.” He said he was still trying to assess the situation and didn’t elaborate further.

It wasn’t immediately clear whether Kim was referring to South Korean military drones, or also drones possibly operated by South Korean civilians.

North Korea is extremely sensitive to any outside criticism of the authoritarian government of leader Kim Jong Un and his family’s dynastic rule over the country.

Since May, North Korea has sent thousands of balloons carrying paper waste, plastic and other trash to drop on the South, in what it described as retaliation against South Korean civilian activists who flew balloons with anti-North Korean propaganda leaflets across the border.

South Korea’s military responded to the North’s balloon campaign by using border loudspeakers to broadcast propaganda and K-pop to North Korea.

The psychological warfare campaigns have further escalated tensions created by Kim’s weapons tests and verbal threats of nuclear conflict against Washington and Seoul. The allies have responded by strengthening their combined military exercises and expanding three-way cooperation with Japan, while also upgrading nuclear deterrence plans built around U.S. strategic assets.

On Wednesday, North Korea said it will 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.

North Korea’s military said in a statement on state media that it will “completely cut off roads and railways” linked to South Korea and “fortify the relevant areas of our side with strong defense structures.”

North Korea called its steps a “self-defensive measure for inhibiting war and defending the security” of the country and accused its rivals of “getting ever more reckless in their confrontational hysteria.” North Korea cited what it called various military exercises in South Korea, the deployment of U.S. strategic assets and its rivals’ harsh rhetoric.

Experts say Kim’s nuclear push is aimed at eventually forcing the United States to accept North Korea as a nuclear power and allowing the North to negotiate security and economic concessions from a position of strength.

In written answers to questions by The Associated Press this month, South Korean President Yoon Suk Yeol said North Korea will likely stage major provocations such as a nuclear test explosion or an intercontinental ballistic missile test around the U.S. presidential election in November to grab Washington’s attention.

Yoon also condemned North Korea over its balloon campaign and warned that it “will face consequences that it will find difficult to withstand” if its balloon activities jeopardize the safety of South Korean people. He didn’t elaborate on what steps his government was considering.

(AP)