Tensions between North Korea and South Korea increased Tuesday, after Pyongyang threatened to move forces into the demilitarized zone between the two countries and blew up their joint liaison office in the North Korean city of Kaesong.

“I feel it is high time to surely break with the South Korean authorities,” said Kim Yo Jong, the increasingly influential sister of North Korean leader Kim Jong Un, according to the BBC.

South Korea on Tuesday confirmed that Pyongyang was responsible for the office’s dramatic demolition, with Kim You-geun, first deputy chief of Seoul’s National Security Council saying it “betrayed the hopes of peace on the Korean Peninsula.”

North Korean state TV aired video of the destruction of the inter-Korean liaison office in Kaesong, North Korea on June 16. (Reuters)

How substantial is this escalation?

The now-demolished liaison office was opened in 2018, following a historic summit between South Korean leader Moon Jae-in and Kim Jong Un.

“From today, South and North Korea can hold face-to-face discussions 24 hours a day and every day of the year on matters concerning improving inter-Korean ties and promoting peace and prosperity on the Korean Peninsula,” South Korean Unification Minister Cho Myoung-gyon said at the time.

Closed over coronavirus concerns since January, it served as a de facto embassy between the two countries, which are technically still at war despite a 1953 armistice.

After 2018, relations seemed to improve, with plans to sign a formal peace treaty. The countries even discussed a bid to host the 2032 Olympics together.

The liaison office was a key element in their plan to broaden cooperation and remained a symbol for those efforts until Tuesday.

What’s behind the rising tensions?

The escalation comes amid plans by North Korean defectors living in South Korea to drop propaganda material in the North. Similar leaflet campaigns in the past have contained anti-Kim messages and were a source of strain, along other moves perceived by Pyongyang as provocations, such as joint South Korean-U. S. military exercises.

But the leaflet drops are not being organized by South Korean officials — who in fact have condemned the plans — prompting analysts to argue the North Korean escalation is the result of broader strain.

North Korea may primarily be seeking to exert pressure on both South Korea and the United States, amid stalled negotiations over North Korean sanctions relief in return for denuclearization progress.

The North has long perused a strategy in which it seems ready to strike a detente, only to return to a more aggressive posture.

Why have denuclearization talks stalled?

Almost exactly two years ago, a historic meeting between President Trump and Kim in Singapore sparked hopes that North Korea could denuclearize. But those initial hopes have proved to be premature. Amid stalled negotiations, North Korea last year imposed a deadline, threatening that the fate of the talks was in the hands of the United States and suggesting that Pyongyang would not make further concessions.

Pyongyang’s deadline passed by the end of last year. U.S. officials rejected it as arbitrary.

In response, North Korea has stepped up provocations over the first half of 2020. Last week, North Korea said it would cut phone hotlines with the South.

Disagreement between the United States and North Korea has in the past largely centered on the degree to which Washington would be willing to lift sanctions in return for denuclearization moves. Last spring, Pyongyang offered to close its Yongbyon nuclear complex, but the United States rejected demands to drop key U.N. sanctions resolutions in return, saying North Korea had to do more to expect such a move.

The Reuters news agency reported last year that U.S. officials have pushed for a “complete, verifiable and irreversible denuclearization” by North Korea.

The stalled talks have prevented previously agreed South and North Korean projects from beginning or resuming, including new infrastructure links.

What is behind the rise of Kim Jong Un’s sister Kim Yo Jong?

The latest escalation followed months of speculation over Kim’s younger sister Kim Yo Jong, as she has taken on a more public role in the regime.

Days before the demolition of the liaison office Tuesday, she threatened its destruction Saturday and called it “useless.”

Her growth in visibility sparked speculation over the North Korean leader’s health in April. Kim Jong Un reemerged in early May, proving theories he was dead or incapacitated to be wrong.

But the rumors highlighted a possible power vacuum in case the leader was to become incapacitated in the future.

Kim Yo Jong’s public profile in North Korea’s tightly controlled propaganda media outlets has been welcomed by some in South Korea who have hopes for closer ties. Amid escalating U.S.-North Korean tensions, Kim Yo Jong traveled to South Korea in 2018 to attend the Winter Olympics in an apparent North Korean effort at the time to drive a wedge between the White House and the government in Seoul.

But others cautioned that her initial charm campaign may not last and that it is unlikely to result in rapprochement. Tuesday’s escalation boosted skepticism that she could come to serve as a moderating force.

Could the escalation lead to another Trump-Kim summit?

Chances of another summit between the two leaders appear to be slim at this point, given prior threats by the Kim regime that “the fate of the future DPRK-U.S. dialogue depends on the U.S. attitude.”

Min Joo Kim in Seoul and Simon Denyer in Tokyo contributed to this article.