Rising tension on the Korean border fuels concern

Tension on the Korean Peninsula is once again ratcheting up, with calls for immediate talks between North and South Korea to avert an accidental military confrontation.

It follows hostile back-to-back statements from Kim Yo Jung – the powerful sister of North Korean leader Kim Jong Un – who said loudspeakers broadcasting anti-South Korea propaganda would be activated within days along the entire 160-mile border. 

She also warned Seoul of "the most horrible and distressing situation" if South Korea continues what Pyongyang called interference in North Korean internal affairs. 

"This is not a threat," she said, "but a clear warning."

On Wednesday, Kim Yo Jung joined senior military officials to visit fortification sites along the border, where she said North Korean tactical units had taken up positions. She accused South Korean forces of broadcasting warning messages and firing warning shots at multiple locations near the border. 

South Korea acknowledged that its forces had fired warning shots, calling them "legitimate and defensive measures."

North Korea expert Bob Carlin, a former U.S. State Department analyst who took part in negotiations with Pyongyang and has followed the country closely for four decades, told CBS News that Kim's statements about "tactical units" are a cause for concern.

"Whether these have heavy weaponry or not, this represents a change in the situation along the front," said Carlin. "Kim Yo Jung also spoke of the possibility of 'deploying more tactical strike means.' This sounds more like artillery and battlefield missile units, and if the decision has been made to move these up, it will be an even more serious change along the front lines."

• Is China worried that North Korea wants "to confront the U.S."? 

Swirling in the background of the rising tension this week were online rumors that North Korea's leader, Kim Jong Un, had died after suffering a brain hemorrhage. The regime discredited the uncorroborated claims by having state media release photos of the 42-year-old dictator touring a clothing and footwear exhibition in Pyongyang with his wife and teenage daughter Kim Ju Ae.

Kim's father, Kim Jong Il, died in 2011 at the age of 69 from a heart attack. His death was only announced to the public two days later. There has been much speculation over who would succeed Kim Jong Un if he were to die suddenly. 

Within the South Korean intelligence community, Kim Ju Ae, who has been a constant figure by her father's side in public in recent years, has been labeled the likely heir apparent. She would be the fourth generation for the Kim dynasty.

But experts believe Kim's sister has been asserting her authority recently, too, and appearances like this week's are part of that effort.

Yang Moo-jin, chair professor at the University of North Korean Studies in Seoul, said Kim Yo Jong's frequent public appearances "serve two purposes: demonstrating to Kim Jong Un that she is working diligently, while also asserting her own profile and influence toward both South Korea and the United States."

Yang said the focus for both governments now should be on resolving the current tension along the demilitarized zone that separates North and South Korea — where some 28,500 U.S. forces are still based more than 70 years after the Korean War.

"The issue of North Korean troops moving southward takes precedence," he told CBS News. "The realistic and rational way to resolve the problem is not through further border fortification, but by sitting down together and finding a mutually acceptable solution through dialogue."

The demilitarized border zone, or DMZ, was established as part of the 1953 armistice agreement between the U.S.-backed South and the China- and Soviet-backed North that ended hostilities in the Korean War. 

Since 2024, North Korea has reinforced its side of the DMZ with mines, barriers and more fencing to establish what it calls a permanent border with South Korea.

Last month, two South Korean soldiers were seriously wounded by what Seoul says were North Korean mines planted as part of those fortifications.

South Korea announced Thursday that it would inform the United Nations Security Council that the mine blasts, in its view, represent a violation of the armistice. Seoul has demanded an apology and the initiation of dialogue with Pyongyang to prevent further escalation.