North Korea has defended its latest nuclear test, citing the fate of two toppled Middle East leaders, while flexing its military muscle by showing TV footage of a submarine-launched missile test.

A commentary published by the official KCNA news agency late Friday said the fate of Saddam Hussein in Iraq and Moamer Kadhafi in Libya showed what happened when countries forsake their nuclear weapon ambitions.

It also warned South Korea, which resumed high-decibel propaganda broadcasts across the inter-Korean border in response to Wednesday's test, that its actions were driving the divided peninsula to "the brink of war".

The commentary said Pyongyang's fourth nuclear test was a "great event" that provided North Korea with a deterrent powerful enough to secure its borders against all hostile forces, including the United States.

"History proves that powerful nuclear deterrence serves as the strongest treasured sword for frustrating outsiders' aggression," it said.

North Korea said the test was of a miniaturised hydrogen bomb -- a claim largely dismissed by experts who argue the yield was far too low for a full-fledged thermonuclear device.

"The Saddam Hussein regime in Iraq and the Kadhafi regime in Libya could not escape the fate of destruction after being deprived of their foundations for nuclear development and giving up nuclear programmes of their own accord," the commentary said.

Both had made the mistake, the commentary argued, of yielding to Western pressure led by a United States bent on regime change.

Asking North Korea to give up its nuclear weapons was as pointless as "wishing to see the sky fall", it said, adding that the entire country was proud of its "H-bomb of justice".

- 'Playing with fire' -

In addition to the KCNA commentary, the state Korean Central TV late Friday released video footage of a purportedly new submarine-launched ballistic missile (SLBM) test.

But South Korean media suggested the footage was an edited compilation of the North's third SLBM test, conducted last month in the Sea of Japan, and a different ballistic missile test from 2014.

The undated footage shows leader Kim Jong-Un, on board a military vessel in a winter coat and a fedora hat, looking on as a missile is launched vertically from underwater and ignites in mid air.

The video then cuts to a rocket flying through the clouds, suggesting the missile was able to reach such altitudes.

But South Korean media said the images of a rocket rising through the clouds were in fact taken from footage of a SCUD missile test broadcast in 2014.

North Korea first announced in May that it had conducted a successful SLBM test, a claim accompanied by pictures of Kim pointing at the missile as it blasted out of the water at a 45-degree angle.

A second SLBM test was carried out off the southeastern port of Wonsan in November but this was apparently a failure as only debris from its casing was seen in the sea and no traces of the flight were detected.

South Korean military officials say the North is continuing to actively pursue the development of SLBMs, which would take its nuclear threat to a new level.

The defiant message and video footage came as the international community scrambled to respond to North Korea's latest test.

While UN Security Council members discuss possible sanctions, world leaders have sought to build a consensus on how best to penalise leader Kim Jong-Un's maverick state.

South Korea on Thursday took unilateral action by switching on giant banks of speakers on the border and blasting a mix of propaganda and K-pop into North Korea.

The same tactic, employed during a dangerous flare-up in cross-border tensions last year, had seen an infuriated Pyongyang threaten artillery strikes against the loudspeaker units unless they were switched off.

At a mass rally held Friday in Pyongyang' Kim Il-Sung square to celebrate the test, senior North Korean ruling party official Kim Ki-Nam said Seoul was once again playing with fire.

"The United States and its puppets have wasted no time in driving the situation on the peninsula to the brink of war, resuming their psychological warfare broadcast," Kim said.