North Korea Sent Excrement Balloons. South Korea’s Response: Blasting BTS Hits.

SEOUL—After enduring days of balloon bombardment from the Kim Jong Un regime, South Korea countered with an airwaves assault of its own: blaring the chart-topping hits of boyband BTS.

For two hours on Sunday, a South Korean loudspeaker near the two countries’ border played a local radio program called “Voice of Freedom,” run by the Seoul military’s psychological warfare unit. North Korean soldiers and border residents would have been within earshot.

The broadcast began with the South Korean national anthem. A news anchor delivered reports that the U.S., South Korea and Japan had condemned the Kim regime’s missile tests and military cooperation with Russia. And then there was K-pop. 

One of the BTS hits chosen was 2020’s “Dynamite,” which has racked up nearly 2 billion views on YouTube and topped the Billboard Hot 100 list. BTS, short for Bangtan Sonyeondan, or “Bulletproof Boy Scouts,” is a seven-member band whose fans worldwide officially dub themselves the “ARMY.” Sung in English, the upbeat Dynamite tune includes references to the basketball star LeBron James, King Kong and the Rolling Stones. 

“So watch me bring the fire,” the song’s lyrics go, “and set the night alight.” 

The two Koreas—which technically remain at war with one another—have embarked in a bizarre tit-for-tat showdown. Neither Pyongyang nor Seoul have expressed a clear-cut desire for actual fighting. But with tensions simmering, the two countries are left with limited ways to express their mutual discontent. 

Starting late last month, the Kim regime flew into South Korea more than a thousand massive balloons carrying bags of trash and excrement. The air deliveries stopped for several days. Then, on Thursday, a South Korean activist group floated balloons containing anti-regime leaflets and foreign media into the North. Pyongyang re-upped its aerial campaign in response.

That prompted Sunday’s loudspeaker broadcast, which also featured a reference to South Korea’s Samsung Electronics being a popular smartphone brand around the world. 

Within hours, Kim’s younger sister, Kim Yo Jong, North Korea’s go-to critic of the U.S. and South Korea, warned of a “new counteraction” should the unwelcomed transmissions continue. “This is the prelude to a very dangerous situation,” Kim Yo Jong said in a late Sunday night statement.

K-pop, in particular, has served as a barometer for relations between the North and South— and is a sore spot for Kim Jong Un, who wants to limit exposure to the outside world inside his impoverished country. In 2015, after loudspeakers boomed out several songs by the girl group “Girls’ Generation,” Kim declared a “semi-war state” and ordered North Korea to fire artillery shells near the border. 

As ties warmed roughly three years later, one of the Girls’ Generation members sang a North Korean song—called “Blue Willow Tree”—in Pyongyang during an inter-Korean summit. Kim and his wife attended the “Spring Is Coming” concert.

During that bout of diplomacy, the two Koreas struck a 2018 military accord meant to tone down military hostilities. That included the South dismantling roughly 40 loudspeakers.

South Korea chose not to broadcast anything on Monday, though could resume at a moment’s notice.

North Koreans were spotted dusting off their own loudspeakers, Seoul’s military said.

Write to Dasl Yoon at dasl.yoon@wsj.com