The man lies down on the debris and a comrade puts a thick concrete block on his chest, before smashing it with a sledgehammer.

The scene was part of a pain-defying display put on by the North Korean army for the opening of a defence exhibition this week that showcased the nuclear-armed country's weapons.

The soldiers -- some in uniform, others topless -- punched their way through layers of concrete bricks, or broke them with their heads.

Others were hammered on their arm or hand, and one lay on a bed of nails to have a block broken on his chest.

Leader Kim looked on clapping and smiling, surrounded by officers and with his sister and close adviser Kim Yo Jong at his side, footage on state broadcaster KCTV showed Tuesday.

Korea has a long tradition of martial arts, and breaking is part of its indigenous sport of taekwondo -- developed by a South Korean general who later fell out with the South's military-backed dictator Park Chung-hee and became a frequent visitor to Pyongyang, where he died in 2002.

It is now often used by the North to symbolise its military prowess.

"These soldiers, embraced and raised by our party, have demonstrated to the whole world the strength, bravery and morale of the Korean People's Army," newsreader Ri Chun-hee -- the North's most famous presenter -- said over the images.

The arms exhibition -- at which Kim blamed the United States for tensions on the peninsula and accused the South of hypocrisy -- is part of the commemorations for the anniversary of the foundation of the ruling Workers' Party.

Kim has overseen rapid progress in Pyongyang's banned nuclear weapons and ballistic missile programmes, which have earned it multiple international sanctions.

And Ri did not forget to declare the source of the participants' strength.

It was "bestowed upon them by our dear leader Kim Jong Un", she said.