A man claiming to be the son of the slain Kim Jong-nam has surfaced, saying he was lying low with his mother and sister, after the murder of his father a month ago.

An official at South Korea's National Intelligence Service said on Wednesday that the man in the video is Kim Han-sol, the 21-year-old son of the North Korean leader's half-brother.

The governments of The Netherlands, China, the United States, and a fourth unnamed country provided emergency humanitarian assistance to protect the family, the group, called Cheollima Civil Defence, said in a statement released on Wednesday alongside the video posted online.

OPINION: Kim Jong-nam attack reveals true nature of North Korea

The elder Kim was killed at Kuala Lumpur International Airport on February 13 by assassins who Malaysian police said used the super-toxic VX nerve agent that killed him within 20 minutes.

The South Korean intelligence official declined to go beyond identifying Kim Han-sol.

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

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

"We hope this gets better soon," he added. He also flashed a copy of his North Korean passport.

The video could not be independently verified.

But according to Reuters news agency, 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 said North Korean leader Kim Jong-un had issued standing orders for the elimination of his elder half-brother.

Diplomatic spat

Meanwhile, in Malaysia, Prime Minister Najib Razak struck a softer tone with North Korea on Wednesday, saying there were no plans to cut diplomatic ties with Pyongyang.

"We are a country that's friendly to them," Najib said, after reassuring Members of Parliament that three embassy staff, six family members, and two other Malaysians in North Korea were safe.

Najib declined to elaborate on the next steps: "If there's any negotiations, we can't do it through the media."

A day earlier, Najib accused North Korea of assassinating Kim Jong-nam and treating Malaysians as "hostages".

Malaysian police have identified eight North Koreans wanted for questioning in connection with the killing, three of them hiding in the North Korean embassy.

In a bid to "ensure the safety" of its diplomats and citizens in Malaysia, North Korea retaliated on Tuesday by banning Malaysians from leaving the country until the case was "properly solved".

Najib denounced that move as an "abhorrent act" and ordered a reciprocal ban. He also for the first time directly accused North Korea of murdering Kim Jong-nam.

"What we are facing now is the result of their action in assassinating their own citizen in Malaysia, on Malaysian soil, using a strictly banned chemical weapon," Najib told state media agency Bernama on Tuesday.