A man claiming to be the son of the poisoned estranged half-brother of North Korea's leader has posted a video online to discuss the killing.

"My father has been killed a few days ago," the man says in English in the 40-second video. "I'm currently with my mother and my sister," he adds, without disclosing his location or who is protecting him.

"We hope this gets better soon."

In the video, he holds up a black North Korean service passport, which are issued to government officials.

Although the details are edited out when he opens it, a North Korean state stamp is visible on one page, as is a line of English text saying the passport's validity has been extended.

North Korea Prison Camps Show all 7 1 /7 North Korea Prison Camps North Korea Prison Camps An overview of Camp 25 Amnesty International/DigitalGlobe North Korea Prison Camps The administration area of Camp 15 Amnesty International/DigitalGlobe North Korea Prison Camps A water treatment system in Camp 25 Amnesty International/DigitalGlobe North Korea Prison Camps Crop fields and, inset, prisoners in Camp 25 Amnesty International/DigitalGlobe North Korea Prison Camps The reported crematorium in Camp 25 Amnesty International/DigitalGlobe North Korea Prison Camps A possible mine Amnesty International/DigitalGlobe North Korea Prison Camps A walled compound in Camp 15 Amnesty International/DigitalGlobe

An official at South Korea's National Intelligence Service told Reuters the man in the video is Kim Han-sol, the 21-year-old son of Kim Jong-nam, who was killed at Kuala Lumpur International Airport last month by assassins using the super-toxic VX nerve agent.

The Transcription Analysis Laboratory, a private voice analysis institute in Seoul, analysed the video and an interview Mr Kim gave to Finnish television in 2012 and said there was a "high probability" the two clips were of the same speaker.

A statement released alongside the video by a group called Cheollima Civil Defense said the governments of the Netherlands, China, the United States, and "a fourth government to remain unnamed" provided emergency humanitarian assistance to protect the family.

It said the organisation responded last month to an emergency request by Kim Jong-nam's family members for "extraction and protection".

It is not clear who is behind the group, which says it can help high-level North Koreans escape the isolated country and hides its digital footprint.

The authors of the statement encouraged people to join their organisation by writing to an email address hosted by a Switzerland-based encrypted email service, and they requested donations via the digital Bitcoin currency.

"The three family members were met quickly and relocated to safety. We have in the past addressed other urgent needs for protection," the Cheollima Civil Defense statement said, adding that the whereabouts of the family will not be addressed.

"Cheollima" is the name given to a mythical horse in Chinese and Korean folklore, said to be able to travel over great distances.

Three arrests amid probe into death of North Korean leader's half-brother

The term is used in North Korean propaganda to symbolise rapid economic development, as well as to name streets, restaurants and other domestic brands

Mr Kim is the son of Kim Jong-nam's second wife, who had been living in the Chinese territory of Macau under Beijing's protection after the family went into exile several years ago.

South Korean intelligence and US officials say Kim Jong-nam's murder was an assassination organised by North Korean agents.

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Malaysian police have identified eight North Koreans wanted for questioning in the case, but the only people charged with the murder so far are an Indonesian woman and a Vietnamese woman who police say wiped the VX nerve agent on the victim's face.

Malaysia is still waiting for DNA samples of the next of kin to officially verify the identity, but no family member has made contact yet.

The Southeast Asian country has said it would only release Kim's body to the next of kin, refusing demands from North Korea to hand over the body without an autopsy.