North Korea threatened on Thursday to end an inter-Korean military agreement reached in 2018 to reduce tensions if the South fails to prevent activists from flying anti-Pyongyang leaflets over the border.

Kim Yo Jong, the powerful sister of North Korea's leader, also said the North could permanently shut a liaison office with the South and an inter-Korean factory park in the border town of Kaesong, which have been major symbols of reconciliation between the Koreas.

North Korean defectors and other activists in recent weeks have used balloons to fly leaflets criticizing the North’s authoritarian leader Kim Jong Un over his nuclear ambitions and dismal human rights record.

FILE - In this Sept. 14, 2018 file photo, South Korea's Unification Minister Cho Myoung-gyon, center left, and Ri Son Gwon, chairman of the North's Committee for the Peaceful Reunification, center right, attend at an opening ceremony for two Koreas' first liaison office in Kaesong, North Korea. North Korea has threatened to end an inter-Korean military agreement reached in 2018 to reduce tensions if the South fails to prevent activists from flying anti-Pyongyang leaflets over the border. Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, said Thursday, June 4, 2020, the North could permanently shut a liaison office with the South and an inter-Korean factory park in the border town of Kaesong, which have been major symbols of reconciliation between the rivals. (Korea PoolYonhap via AP, File)

FILE - In this Sept. 14, 2018 file photo, South Korea's Unification Minister Cho Myoung-gyon, center left, and Ri Son Gwon, chairman of the North's Committee for the Peaceful Reunification, center right, attend at an opening ceremony for two Koreas' first liaison office in Kaesong, North Korea. North Korea has threatened to end an inter-Korean military agreement reached in 2018 to reduce tensions if the South fails to prevent activists from flying anti-Pyongyang leaflets over the border. Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, said Thursday, June 4, 2020, the North could permanently shut a liaison office with the South and an inter-Korean factory park in the border town of Kaesong, which have been major symbols of reconciliation between the rivals. (Korea PoolYonhap via AP, File)

Sending balloons across the border has been a common activist tactic for years, but North Korea considers it an attack on its government. It wants them banned, but Seoul refuses and says the activists and defectors are exercising free speech.

In her statement released through state media, Kim Yo Jong called those defectors “human scum” and “mongrel dogs” who betrayed their homeland and said it was “time to bring their owners to account,” referring to the government in Seoul.

“(South Korean) authorities will be forced to pay a dear price if they let this situation go on while making sort of excuses,” she said.

FILE - In this March 2, 2019, file photo, Kim Yo Jong, sister of North Korea's leader Kim Jong Un attends a wreath-laying ceremony at Ho Chi Minh Mausoleum in Hanoi, Vietnam. North Korea has threatened to end an inter-Korean military agreement reached in 2018 to reduce tensions if the South fails to prevent activists from flying anti-Pyongyang leaflets over the border. The powerful sister said Thursday, June 4, 2020, the North could permanently shut a liaison office with the South and an inter-Korean factory park in the border town of Kaesong, which have been major symbols of reconciliation between the rivals.  (Jorge SilvaPool Photo via AP, File)

FILE - In this March 2, 2019, file photo, Kim Yo Jong, sister of North Korea's leader Kim Jong Un attends a wreath-laying ceremony at Ho Chi Minh Mausoleum in Hanoi, Vietnam. North Korea has threatened to end an inter-Korean military agreement reached in 2018 to reduce tensions if the South fails to prevent activists from flying anti-Pyongyang leaflets over the border. The powerful sister said Thursday, June 4, 2020, the North could permanently shut a liaison office with the South and an inter-Korean factory park in the border town of Kaesong, which have been major symbols of reconciliation between the rivals. (Jorge SilvaPool Photo via AP, File)

“If they fail to take corresponding steps for the senseless act against the fellow countrymen, they had better get themselves ready for possibility of the complete withdrawal of the already desolate Kaesong Industrial Park following the stop to tour of (Diamond Mountain), or shutdown of the (North-South) joint liaison office whose existence only adds to trouble, or the scrapping of the (North-South) agreement in military field which is hardly of any value.”

In a separate statement, the international affairs department of the North’s ruling Workers’ Party accused U.S. Secretary of State Mike Pompeo of spewing “rubbish” over his critical comments toward Beijing, which is Pyongyang’s biggest ally.

In a Fox News interview on Sunday, Pompeo said the Chinese Communist Party was putting Americans at risk because it has come to “view itself as intent upon the destruction of Western ideas, Western democracies, Western values.”

The department’s unidentified spokesman also commented on the intensifying protests in the United States over the death of George Floyd, saying that the unrest exposes harsh realities in America.

“Demonstrators enraged by the extreme racists throng even to the White House. This is the reality in the U.S. today. American liberalism and democracy put the cap of leftist on the demonstrators and threaten to unleash even dogs for suppression.”

South Korea’s government didn’t immediately react to Kim Yo Jong’s comments.

It has touted the military agreement, reached during the third summit between Kim Jong Un and South Korean President Moon Jae-in, as a major step in the peace process.

The Koreas had agreed to jointly search for human remains from the 1950-53 Korean War and take steps to reduce conventional military threats, such as establishing buffer and no-fly zones. They also removed some front-line guard posts and jointly surveyed a waterway near their western border to allow freer civilian navigation.

However, the North has been less enthusiastic about upholding inter-Korean agreements as the larger nuclear talks with the U.S. stalemate. North Korea has suspended virtually all cooperation with the South, while also pressuring Seoul to break away from Washington and restart the joint economic projects, which would breathe life into the North’s broken economy.

“If they truly value the (North-South) agreements and have a will to thoroughly implement them, they should clear their house of rubbish,” said Kim Yo Jong, who’s considered her brother’s closest confidant.

The liaison office in Kaesong has been closed since late January after the Koreas agreed to temporarily shut down until the coronavirus outbreak is controlled.

The North has also postponed plans to tear down South Korean-made hotels and other facilities at the North’s Diamond Mountain resort as part of its virus-prevention efforts. It has said there hasn’t been a single case of COVID-19 on its territory, a claim widely disbelieved.

Kim Yo Jong’s comments follow months of frustration over the South’s unwillingness to defy U.S.-led international sanctions against the North and resume South Korean tours at the site.

After years in her brother’s shadow, Kim Yo Jong emerged as part of her brother's diplomatic efforts in 2018. She was the first member of the North’s Kim dynasty to travel to the South for the opening ceremony of the Winter Olympics in February 2018. She took her place among global dignitaries before conveying to Moon her brother’s desire for a summit.

As regional diplomacy has slowed in recent months due to the coronavirus, she has been issuing her first public statements, ridiculing Seoul for protesting a North Korean military drill but praising President Donald Trump for offering to help the North with anti-virus efforts.