Video has emerged of a man claiming to be the son of the slain, estranged half- brother of North Korea's leader, who says he is lying low with his mother and sister.

The video was posted online by a group that said it helped rescue them after Kim Jong Nam's murder a month ago following an emergency request by family members for "extraction and protection".

The governments of Netherlands, China, the US and a fourth unnamed country provided emergency assistance to protect the family, the group, called Cheollima Civil Defense, said in a statement released on Wednesday along with the video.

An official at South Korea's National Intelligence Service said the man in the video was Kim Han-sol, the 21-year-old son of Kim Jong-nam, who was killed at Kuala Lumpur International Airport on February 13 by assassins who Malaysian police say used a super-toxic nerve agent.

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During the 40-second video, the man says his father was killed a few days ago.

"I'm currently with my mother and my sister," he says, without disclosing his location or who he was living with.

"We hope this gets better soon."

Reuters could not independently verify the video but the man closely resembled Kim Han-sol, who was last interviewed on camera in 2012 by former Finnish defence minister Elisabeth Rehn.

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

South Korean intelligence officers say North Korean leader Kim Jong-un had ordered the elimination of his elder half-brother.

- additional reporting Reuters