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 Muammar Gaddafi 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 Gaddafi 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".