Kim Jong Nam's son appeared to break his silence Tuesday in a video posted to YouTube, giving some of the first clues about the whereabouts of the victim's immediate family after the murder last month.

Kim Jong Nam, the North Korean dictator Kim Jong Un's half-brother, had three children with two women living in Beijing and Macau. In the video, a man claiming to be his son Kim Han Sol said he, his mother and his sister were safe.

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"My father has been killed a few days ago," the man said in English in the 40-second clip. "I'm currently with my mother and my sister. ... We hope this gets better soon."

Malaysian authorities have charged two women -- one Indonesian, one Vietnamese -- with murder for allegedly swiping Kim Jong Nam's face with VX nerve agent as he waited at a Kuala Lumpur airport for a flight home to Macau on Feb. 13. He was dead within 20 minutes.

Malaysia has sought seven North Korean suspects, including an embassy official. The investigation has infuriated North Korea, which has dismissed the inquiry as politically motivated.

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The man in the video didn't talk about his family's whereabouts or how they were being protected. The clip appeared on the YouTube channel of Cheollima Civil Defense, which described itself as a group helping North Korean defectors.

The group said on its website that it responded to an "emergency request" by three members of Kim Jong Nam's family and relocated them. The group expressed gratitude to the Netherlands, China, the United States and a "fourth government to remain unnamed" for providing assistance in protecting the three, Sky News reported.

The audio was cut during part of the clip, and information was blacked out on a passport the man held to the camera.

Meanwhile, Malaysia's prime minister said Wednesday that relatives of Kim Jong Nam may be too scared to help police investigating his mysterious poisoning death. Prime Minister Najib Razak spoke a day after a stunning diplomatic breakdown involving the investigation into Kim Jong Nam's killing, with North Korea barring Malaysians from leaving its territory and Malaysia responding in kind.

While on Tuesday he denounced North Korea for "effectively holding our citizens hostage," Najib said Wednesday that his country still wanted to negotiate.

"You must appreciate -- I know you're hungry for news -- but you must appreciate that this is a sensitive matter and that sometimes it's best conducted in secrecy so that we can achieve the desired result," Najib told reporters. He said Malaysians in North Korea are going about their lives normally, and he was not worried about their safety.

Najib also said investigators were still trying to get DNA samples from Kim's immediate family to formally identify his body. "Maybe they are scared to come forward," he added.

South Korea's Unification Ministry said it had no knowledge of the Cheollima group, but an official at South Korea's National Intelligence Service said the NIS had determined that the man in the video is Kim Han Sol. The public affairs official, who spoke on condition of anonymity, citing department rules, didn't explain how his agency confirmed the man's identity.

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

Malaysian investigators said the two women who poisoned Kim Jong Nam were recruited by a team of North Koreans. North Korea has denied any responsibility and accused Malaysia of being swayed by the North's enemies.

Officials in Kuala Lumpur say there are 11 Malaysians currently in North Korea: three working at the embassy, two U.N. employees and six family members. About 1,000 North Koreans are believed to be in Malaysia, until recently one of the few countries where North Koreans could travel without a visa.

Four of the North Korean suspects being sought by Malaysia are believed to have left the country the day Kim Jong Nam was killed. Police say the remaining three suspects, including a North Korean diplomat, are believed to be in hiding at the North Korean Embassy in Kuala Lumpur, a hulking concrete mansion behind a wall streaked with water stains.

The Associated Press contributed to this report.

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