Video footage released by an organisation that works with North Korean defectors shows North Korean authorities publicly sentencing two teenagers to 12 years' hard labour for watching K-pop.

The footage, which shows the two 16-year-olds in Pyongyang convicted of watching South Korean movies and music videos, was released by the South and North Development (SAND) Institute.

Reuters was unable to independently verify the footage, which was first reported by the BBC.

North Korea has for years imposed tough sentences on anyone caught enjoying South Korean entertainment or copying the way South Koreans speak in a war on outside influences since a sweeping new "anti-reactionary thought" law was imposed in 2020.

"Judging from the heavy punishment, it seems that this is to be shown to people across North Korea to warn them. If so, it appears this lifestyle of South Korean culture is prevalent in North Korean society," said Choi Kyong-hui, president of SAND and Doctor of Political Science at Tokyo University, who defected from North Korea in 2001.

"I think this video was edited around 2022... What is troublesome for (North Korean leader) Kim Jong Un is that Millennials and Gen Z young people have changed their way of thinking. I think he's working on turning it back to the North Korean way."

The video, made by North Korean authorities, shows a large public trial in which the two students in grey scrubs are handcuffed while watched by about 1,000 students in an amphitheatre. All the students, including the two 16-year-olds, are wearing face masks, suggesting the footage was shot during the COVID pandemic.

The students were sentenced, according to the video, after being convicted of watching and spreading South Korean movies, music and music videos over three months.

"They were seduced by foreign culture... and ended up ruining their lives," the narrator states, as the video cut away to young girls being handcuffed and Pyongyang women wearing South Korean fashion and hairstyles.

Reclusive North Korea and the rich, democratic South are technically still at war after their 1950-53 conflict ended in a truce, not a peace treaty, and are divided by a heavily fortified demilitarized zone (DMZ).