Footage released last week by North Korea purporting to show the firing of a submarine-launched ballistic missile appears to be fake, according to US experts.
In defiance of a UN ban, North Korea said it has ballistic missile technology which would allow it to launch a nuclear warhead from a submarine. However, analysis of North Korean state media images casts doubt on the claim.
North Korea released the submarine launch footage after it separately conducted a fourth nuclear weapons test last Wednesday (local time).
North Korean state television aired footage on Friday of the submarine test said to have taken place in December.
South Korea's military said on Saturday that North Korea appeared to have modified the video and edited it with Scud missile footage from 2014.
An analysis by the California-based James Martin Center for Nonproliferation Studies shows two frames of video from state media where flames engulf the missile and small parts of its body break away.
"The rocket ejected, began to light, and then failed catastrophically," Melissa Hanham, a senior research associate at the Middlebury Institute's CNS, said in an email.
"North Korea used heavy video editing to cover over this fact."
In an analysis on the 38 North monitoring website, John Schilling, a specialist in satellite and launch vehicle propulsion systems, said it appeared from the video that the launch was conducted from a submerged barge.
"An initial operational capability of a North Korean ballistic-missile submarine is not expected before 2020," he said.
In Washington, the US House of Representatives voted on Tuesday to pass legislation that would broaden sanctions over North Korea's nuclear program.
It was introduced in early 2015, but was not brought up for a vote until after Pyongyang announced last week it had tested a hydrogen bomb.
North Korea's claim that its most recent nuclear test was of a more advanced and powerful hydrogen bomb drew scepticism from US government and experts.