South Korea has confirmed that the half-brother of North Korea's leader Kim Jong-un has been killed in Malaysia.
No motive has been confirmed and the attackers have not been identified.
South Korea's acting President Hwang Kyo-ahn said if North Korea was found to be responsible, it would show its "brutality and inhumane nature".
It would be the most high-profile death at the hands of the North Korean leadership since Kim Jong-un's uncle, Chang Song-thaek, was executed in 2013.
Mr Hwang said South Korea was "keeping close tabs on North Korea's movements".
Women seen in footage
Mr Kim was attacked while preparing to board a flight home to Macau from the budget terminal outside Kuala Lumpur. His death was only made public on Tuesday.
The chief police officer of Royal Malaysian police, Datuk Sri Abu Samad, has said investigations are still in progress and that a post-mortem examination is expected to be completed soon.
He said Malaysian officials had not yet formally confirmed the identify of the deceased, as he was using a passport under a different name, Kim Chol.
In response to reports that North Korea had asked to claim the body, he said there had been no official request.
Police are studying security camera footage from the airport. Images circulating in the media have focused on two women seen alongside Mr Kim, who were later seen leaving the scene in a taxi.
Unnamed US government sources have said they believe he was poisoned by North Korean agents.
The director of the National Intelligence Service (NIS), Lee Byung-ho, told South Korean MPs that Pyongyang had wanted to kill Kim Jong-nam for several years, but that he was being protected by China.
What happened?
Kim Jong-nam was attacked at about 09:00 (01:00 GMT) on Monday while waiting at the budget terminal of Kuala Lumpur International Airport for a 10:00 flight to Macau, Malaysia's Star newspaper reports, quoting police.
Exactly how the attack unfolded is still unclear. Officials and witnesses have variously said he was splashed with a chemical or had a cloth placed over his face. Earlier reports spoke of a "spray" being used or a needle.
He died on the way to hospital.
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