North Korea has vowed to ignore the result of a Malaysian post mortem on Kim Jong-un's assassinated brother.

Saying it would "categorically reject" the result, Pyongyang demanded the body of Kim Jong-Nam be released immediately. Malaysia had earlier said that the body will not be released until his family have provided DNA samples.

Detectives in Kuala Lumpur are trying to get to the bottom of the cloak-and-dagger murder that South Korea says was carried out by poison-wielding female agents working for their secretive northern neighbour.

North Korean leader Kim Jong Un, left, is suspected of ordering the murder of his half-brother, right. Photo / AP
North Korean leader Kim Jong Un, left, is suspected of ordering the murder of his half-brother, right. Photo / AP

China Press, a Chinese-language newspaper in Malaysia, reported what Kim Jong-Nam told an official behind a counter shortly before he died.

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"Very painful, very painful, I was sprayed liquid," the 45-year-old is reported to have said to the unnamed woman as he collapsed.

Forensic specialists on Friday began testing samples from the dead man's body to try to determine the toxin that was apparently sprayed in his face as he readied to board a plane earlier this week.

"The Malaysian side forced the post mortem without our permission and witnessing, we will categorically reject the result of the post mortem conducted unilaterally excluding our attendance," the North Korean ambassador Kang Chol said in a statement read to the media outside the hospital late on Friday.

But Kuala Lumpur has stood firm, and said on Friday it would not release the body until procedures were complete.

"So far no family member or next of kin has come to identify or claim the body. We need a DNA sample of a family member to match the profile of the dead person," Selangor state police chief Abdul Samah Mat told AFP.

The woman (left) seen in CCTV images wearing a white top with the letters
The woman (left) seen in CCTV images wearing a white top with the letters "LOL" emblazoned on the front reportedly returned to a hotel after the killing showing no sign of stress. Photo / AP

Meanwhile, a 28-year-old woman arrested in connection with the killing reportedly cut her hair,

carried a wad of cash and moved hotels in the days leading up to the assassination.

The woman seen in CCTV images from the airport wearing a white top with the letters "LOL" emblazoned on the front returned to a hotel after the killing showing no sign of stress, according to the receptionist.

The woman, who was carrying a Vietnamese passport which identified her as Doan Thi Huong, has reportedly told police she thought she was taking part in prank.

A woman wearing a yellow top, fourth from left, suspected of involvement in the apparent assassination is escorted by Malaysian officials to a vehicle in Kuala Lumpur. Photo / AP
A woman wearing a yellow top, fourth from left, suspected of involvement in the apparent assassination is escorted by Malaysian officials to a vehicle in Kuala Lumpur. Photo / AP

However, staff at two hotels in a rundown area near the airport gave details of Doan's movements before the killing that appeared both calm and deliberate. A private investigator told Reuters her behaviour bore the hallmarks of an intelligence operative.

Police, meanwhile, were questioning another women - travelling on an Indonesian document - as well as a Malaysian man.

Officers arrested Muhammad Farid Bin Jalaluddin, a 26-year-old Malaysian man on Wednesday. He led them to his girlfriend, a 25-year-old Indonesian national named Siti Aishah.

Aishah's family in Jakarta expressed their shock over her arrest, with her former father-in-law saying there was "no way such a nice person would do that".

Passengers line up at the check-in counter in the terminal of Kuala Lumpur International Airport where Kim Jong Nam died. Photo / AP
Passengers line up at the check-in counter in the terminal of Kuala Lumpur International Airport where Kim Jong Nam died. Photo / AP

"I could not believe it because she was a good person," said Tija Liang Kiong, 56.

Indonesian Vice President Jusuf Kalla said Aishah appeared to be the "victim of a scam or a fraud" who thought she was taking part in a reality show involving hidden cameras.

Indonesian embassy officials said they were providing Aishah with legal assistance.

The drama erupted on Monday morning as Jong-Nam, the estranged elder brother of Kim Jong-un, readied to board a plane to Macau.

Malaysian police say the chubby 45-year-old was jumped by two women who squirted some kind of liquid in his face.

Jong-Nam told staff he was suffering from a headache and was taken to the airport clinic grimacing in pain, according to Malaysian media citing CCTV footage from the airport.

One of the women walked to a taxi rank immediately after the attack, according to the same footage.

He was rushed to hospital suffering from a seizure but was dead before he arrived.

South Korea has pointed the finger of blame at the North, citing a "standing order" from Jong-Un to kill his sibling and a failed assassination bid in 2012 after he criticised the regimen.

Kim Jong-Nam, centre, seen in 2007 walking among journalists upon his arrival at Beijing's international airport. Photo / AP
Kim Jong-Nam, centre, seen in 2007 walking among journalists upon his arrival at Beijing's international airport. Photo / AP

A Japanese journalist who knew and wrote a book on Jong-Nam on Friday said he was a courageous man who sought to reform his country.

"Even if it put him in danger, he wanted to tell his opinions to Pyongyang through me or other media," Yoji Gomi said in Tokyo.

Pyongyang has made no comment on the killing, and there has been no mention of it in North Korean media.

AFP correspondents in Pyongyang say celebrations to mark the birthday of Kim Jong-il, the late father of both men, have gone ahead without reference to the death.

Selangor state police chief Abdul Samah earlier told AFP he was looking for several more suspects, but declined to say how many were being sought.

Firstborn Jong-Nam was once thought to be the natural successor to his father, but on Kim Jong-il's death in 2011 the succession went to Jong-Un, who was born to the former leader's third wife.

Reports of purges and executions have emerged from the current regimen as Jong-Un tries to strengthen his grip on power in the face of international pressure over nuclear and missile programs.

The most notable of these was the 2013 execution for treason of the young leader's influential uncle, Jang Song-Thaek.