Experts analysing footage released by North Korea last week showing the firing of a submarine-launched ballistic missile say the images appear to be faked.

Key points: Specialists say North Korea heavily edited footage to fake a successful submarine-launched ballistic missile test

Specialists say North Korea heavily edited footage to fake a successful submarine-launched ballistic missile test They say analysis shows two frames where the missile catches fire and explodes

They say analysis shows two frames where the missile catches fire and explodes Experts also believe the launch came from a submerged barge rather than a submarine

In defiance of a United Nations ban, North Korea said it tested ballistic missile technology that would allow it to launch a nuclear warhead from a submarine.

North Korea released the submarine launch footage after it separately conducted a fourth nuclear weapons test on January 6.

Two days later, North Korean state television aired footage of the submarine test which it said took place in December.

Unlike a previous submarine-launched ballistic missile (SLBM) test in May, it was not announced at the time.

At the weekend, South Korea's military said North Korea appeared to have modified the video and edited it with Scud missile footage from 2014.

However, an official said the ejection technology might have improved since that test.

Now, analysis by the California-based James Martin Centre for Nonproliferation Studies (CNS) shows two frames of the state media video where flames engulf the missile and small parts of its body break away.

"The rocket ejected, began to light, and then failed catastrophically," CNS senior research associate Melissa Hanham said.

"North Korea used heavy video editing to cover over this fact."

Ms Hanham said North Korea state media used different camera angles and editing to make it appear the launch was several continuous launches, when in fact it was a single event.

Launch likely from barge, not submarine: expert

She said the CNS study showed editors used rudimentary techniques to crop and flip old video footage of an earlier SLBM test and Scud missile launch.

H-bomb or A-bomb? Sorry, this video has expired Hydrogen bomb explained Simply put, atomic bombs' nuclear fission is the process of splitting atomic nuclei, while hydrogen bombs' fusion is joining them

Simply put, atomic bombs' nuclear fission is the process of splitting atomic nuclei, while hydrogen bombs' fusion is joining them In H-bombs, TNT ignites an A-bomb to detonate adjacent to a fusion fuel such as tritium, deuterium or lithium deuteride, compressing them at extreme pressures and at a very rapid rate to start a fusion reaction

In H-bombs, TNT ignites an A-bomb to detonate adjacent to a fusion fuel such as tritium, deuterium or lithium deuteride, compressing them at extreme pressures and at a very rapid rate to start a fusion reaction Nuclear fusion is the process that occurs in the heart of the sun, and requires immense temperatures to ignite

Nuclear fusion is the process that occurs in the heart of the sun, and requires immense temperatures to ignite H-bombs, thermonuclear bombs and fusion bombs can be thousands of times more powerful than atomic bombs, atom bombs, A-bombs, or fission bombs Source: ABC/AFP

John Schilling, an aerospace engineer who is a specialist in satellite and launch vehicle propulsion systems, said it appeared from the video that the launch was conducted from a submerged barge rather than a submarine.

"The failed launch, combined with testing from a barge, shows that North Korea still has a long way to go to develop this system," he said in an analysis on the 38 North monitoring website.

"An initial operational capability of a North Korean ballistic-missile submarine is not expected before 2020."

There has also been scepticism from the US Government and experts about North Korea's other claim that its most recent nuclear test was of a more advanced and powerful hydrogen bomb.

Nuclear experts have also cast doubt about North Korea's recent claim that it had successfully tested a miniaturised hydrogen bomb, saying the detected seismic activity suggested a less powerful device.

Crispin Rovere, an Australia-based nuclear policy and arms control specialist, said the 5.1-magnitude tremor detected at the North's Punggye-ri nuclear test site was too small to support Pyongyang's claim.

"The seismic data that's been received indicates that the explosion is probably significantly below what one would expect from an H-bomb test," Mr Rovere said.

"So, initially, it seems to be that they've successfully conducted a nuclear test but unsuccessfully completed the second-stage hydrogen explosion."

This test came just two days before leader Kim Jong-un's birthday. Analysts said the leader had been looking for a major achievement to highlight at a rare ruling party congress scheduled for May, the first gathering of its kind for 35 years.

Reuters