The estranged half-brother of North Korean leader Kim Jong-Un died on Monday after being sprayed with an unidentified chemical at Kuala Lumpur International Airport.

South Korea and the US have said he was assassinated by North Korean agents, and two women are believed to be responsible for the killing.

The four suspects, who are all male and aged between 33 and 57, flew out of the country on the same day that Mr Kim died, police chief Tan Sri Noor Rashid Ibrahim told a news conference.

But police have not revealed the flight's destination, only that they are working with Interpol to track them down.

In addition, another three North Koreans are being sought to assist police with their enquiries.

It comes after officers arrested a North Korean man on Friday in connection with the murder, 46-year-old IT worker Ri Jong Hol.

Two female suspects, one from Indonesia and the other carrying Vietnamese travel documents, were detained earlier this week, along with a Malaysian man who is the boyfriend of one of the suspects.

Pyongyang has demanded Mr Kim's body be returned but Malaysia has refused the request, saying it must remain in the country until identified through a DNA sample from a family member.

Police said on Sunday a family member has yet to come forward, and that a cause of death has still not been established.

North Korea has said it will reject Malaysia's post-mortem report and accused the country of "colluding with outside forces", a veiled reference to South Korea.

Mr Kim was known to advocate reform of North Korea's authoritarian regime and opposed its dynastic succession policy.

South Korean intelligence chiefs believe his killing was an assassination ordered by Kim Jong-Un some time ago because he perceived his half-brother to be a threat.

(Additional reporting from IRN)