Astonishing video has emerged of bare-chested North Korean soldiers bashing bricks and each other in a “self-defence” training exhibition watched by a laughing leader Kim Jong-un.

The bizarre exhibition took place on Monday, and was later broadcast by North Korea’s state-run media.

The 133-second clip was shared by North Korea-focused journalist and researcher Martyn Williams, and has been widely shared and viewed since it was uploaded onto Twitter.

It shows Mr Kim and other high-ranking North Koreans revelling in the display – smiling and clapping – as the troops show off their martial arts.

There are two-footed jump kicks and much breaking of what looks like concrete tiles. Another segment shows a shirtless soldier being hit with poles by others, breaking between hits to roar in a performative style.

In the final act, a shirtless soldier smashes two glass bottles together and then lies in the broken pieces.

Tweet from @martyn_williams

The viral video came as Mr Kim Jong-un vowed to build an “invincible” military, as he accused the US of creating tensions and failing to prove it had no hostile intent towards Pyongyang.

In an apparent continued effort to drive a wedge between Washington and Seoul, Mr Kim also said his drive to build up his military was not targeted at South Korea and that there should not be another war pitting Korean people against each other.

He gave the speech on Monday at an event meant to mark the previous day’s 76th birthday of the ruling Workers’ Party.

The event featured an array of new weapons, including intercontinental ballistic missiles that North Korea has already test-launched or displayed during a military parade.

“The US has frequently signalled it’s not hostile to our state, but there is no action-based evidence to make us believe that they are not hostile,” Mr Kim said, according to the official Korean Central News Agency.

“The US is continuing to create tensions in the region with its wrong judgements and actions.”

Calling the US a “source” of instability on the Korean Peninsula, Mr Kim said his country’s most important objective was possessing an “invincible military capability”.

He accused South Korea of hypocrisy because it criticised the North’s weapons development as provocations while spending heavily to increase its own military capabilities, including buying advanced US stealth fighters.

But he maintained his military did not target the south.

“I say once again that South Korea isn’t the one that our military forces have to fight against,” Mr Kim said.

“We aren’t strengthening our defence capability because of South Korea. We shouldn’t repeat a horrible history of compatriots using force against each other.”

Seoul’s Defence Ministry said South Korean and US intelligence authorities were analysing the North Korean weapons displayed.

“Basically, North Korea wants to send this message: ‘We’ll continue to develop new weapons and arm ourselves with nuclear force, so don’t slap sanctions with these as we can’t agree on the double standards,”‘ Yang Wook, a military expert who teaches at South Korea’s Hannam University, said.

-with AAP