North Korea leader defends 'hydrogen bomb' test

Pyongyang on Wednesday carried out its fourth nuclear test, angering the international community and raising tensions with neighbouring South Korea.

The test was "a self-defensive step for reliably defending the peace on the Korean Peninsula and the regional security from the danger of nuclear war caused by the US-led imperialists," Kim was quoted as saying.

"It is the legitimate right of a sovereign state and a fair action that nobody can criticise," he added, according to the official Korean Central News Agency (KCNA).

The North regularly accuses the US and its ally South Korea of warmongering.

Kim's comments came during a visit to the Ministry of People's Armed Forces to congratulate them on the "successful" detonation, KCNA said, without giving the date of the visit.

They echo an official commentary published late Friday, which cited toppled leaders Saddam Hussein in Iraq and Muammar Gaddafi in Libya as examples of what happens when countries forsake their nuclear ambitions.

The test has angered world powers, including the North's key ally China, and the UN Security Council has said it will roll out new measures to punish the maverick state.

South Korea has resumed high-decibel propaganda broadcasts across the border in response, which the North said were driving the divided peninsula to "the brink of war".

North Korea claimed it used a miniaturised hydrogen bomb, which is far more powerful than other nuclear devices, although experts said seismic activity suggested it was not strong enough.

The test came just two days before Kim's 33rd birthday and ahead of a rare ruling party congress scheduled to take place in May - the first such gathering for 35 years.

The North is expected to lay out a range of key policies during the congress, which Kim said will be a "historic turning point in accomplishing the revolutionary cause of Juche (self-independence)".

"Let us defend the 7th Congress of the Workers' Party of Korea by strengthening the political and military might of the People's Army in every way", Kim said, adding that strengthening the military is a priority.

The state Korean Central TV late on 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.