The powerful sister of North Korean leader Kim Jong Un threatened military action against South Korea as she bashed Seoul on Saturday over declining bilateral relations and its inability to stop activists from floating anti-Pyongyang leaflets across the border.

Describing South Korea as an “enemy”, Kim Yo Jong repeated an earlier threat she had made by saying Seoul will soon witness the collapse of a “useless” inter-Korean liaison office in the border town of Kaesong.

Kim, who is first vice department director of North Korea's ruling Workers’ Party’s Central Committee, said she would leave it to North Korea’s military leaders to carry out the next step of retaliation against the South.

“By exercising my power authorised by the supreme leader, our party and the state, I gave an instruction to the arms of the department in charge of the affairs with enemy to decisively carry out the next action,” she said in a statement carried by the North’s official Korean Central News Agency.

“If I drop a hint of our next plan the [South Korean] authorities are anxious about, the right to taking the next action against the enemy will be entrusted to the General Staff of our army,” she said.

“Our army, too, will determine something for cooling down our people’s resentment and surely carry it out, I believe.”

Kim’s harsh rhetoric demonstrates her elevated status in North Korea’s leadership. Already seen as the most powerful woman in the country and her brother’s closest confidant, state media recently confirmed that she is now in charge of relations with South Korea.

The liaison office in Kaesong, which has been shut since January due to coronavirus concerns, was set up as a result of one of the main agreements reached in three summits between Kim Jong Un and South Korean President Moon Jae-in in 2018.

Moon’s government had lobbied hard to set up nuclear summits between Kim and United States President Donald Trump, who have met three times since 2018.

At the same time, Moon also worked to improve inter-Korean relations.

But North Korea in recent months has suspended virtually all cooperation with the South while expressing frustration over the lack of progress in its nuclear negotiations with the Trump administration.

Over the past week, the North declared that it would cut off all government and military communication channels with the South and threatened to abandon key inter-Korean peace agreements reached by their leaders in 2018.

They include a military agreement in which the Koreas committed to jointly take steps to reduce conventional military threats, such as establishing border buffers and no-fly zones.

They also removed some front-line guard posts and jointly surveyed a waterway near their western border in an unrealised plan to allow freer civilian navigation.

In an earlier statement last week, Kim Yo Jong said that the North would scrap the military agreement, “which is hardly of any value”, while calling North Korean defectors who send leaflets from the South “human scum” and “mongrel dogs.”

Her comments on Saturday came hours after a senior North Korean Foreign Ministry official said that Seoul should drop “nonsensical” talk about the North’s denuclearisation, and that his country would continue to expand its military capabilities to counter what it perceives as threats from the US.

In response to North Korea’s anger over the leaflets, South Korea’s government has said it would press charges against two defector groups that have been carrying out border protests.

The South also said it would push new laws to ban activists from flying the leaflets across the border, but there’s been criticism over whether Moon’s government is sacrificing democratic principles to keep alive his ambitions for inter-Korean engagement.

For years, activists have floated huge balloons into North Korea carrying leaflets criticising Kim Jong Un over his nuclear ambitions and dismal human rights record.

The leafleting has sometimes triggered a furious response from North Korea, which bristles at any attempt to undermine its leadership.

While Seoul has sometimes sent police officers to block the activists during sensitive times, it had previously resisted North Korea’s calls to fully ban them, saying they were exercising their freedom.

Activists have vowed to continue with the balloon launches.

But it’s unlikely that North Korea’s belligerence is about just the leaflets, analysts say.

The North has a long track record of dialing up pressure on the South when it doesn’t get what it wants from the US.

Its threats to abandon inter-Korean agreements came after months of frustration over Seoul’s refusal to defy US-led sanctions and restart joint economic projects.

Some experts say North Korea, which has mobilised people for massive demonstrations condemning defectors, is deliberately censuring the South to rally its public and shift attention away from a bad economy, which likely has worsened during the Covid-19 pandemic.

It’s unclear what kind of military action the North would take against the South, although weapons tests are an easy guess.

Kim Dong yub, an analyst from Seoul’s Institute for Far Eastern Studies, said North Korea could also be “planning something” near the countries’ disputed western maritime border, which has occasionally been the scene of bloody clashes over the years.

Nuclear talks faltered at Kim Jong Un’s second summit with Trump in Vietnam in February last year after the US rejected North Korea’s demands for major sanctions relief in exchange for a partial surrender of its nuclear capabilities.

Trump and Kim met for a third time that year in June at the border between North and South Korea and agreed to resume talks.

But an October working-level meeting in Sweden broke down over what the North Koreans described as the Americans’ “old stance and attitude”.

On the two-year anniversary of the first Kim-Trump meeting, North Korean Foreign Minister Ri Son Gwon said on Friday that the North would never again gift Trump with high-profile meetings he could boast as foreign policy achievements unless it gets something substantial in return.