Kuala Lumpur (AFP) - Malaysian police probing the killing of the half-brother of North Korea's leader arrested a woman Wednesday as they tried to unravel a Cold War-style assassination the South said was carried out by Pyongyang's agents.

As Seoul pointed the finger at poison-wielding female spies from North of their shared border, police in Kuala Lumpur said they were holding a woman with a Vietnamese passport.

Her arrest came around 24 hours after news broke of the death of Kim Jong-Nam, the elder sibling of North Korean leader Kim Jong-Un, with reports saying female assassins had sprayed toxins in his face at Kuala Lumpur International Airport.

CCTV images that emerged in Malaysian media, purportedly of one of the suspects, showed an Asian woman wearing a white top with the letters "LOL" emblazoned on the front.

Malaysian police chief Khalid Abu Bakar said 28-year-old Doan Thi Huong was arrested at the airport on Wednesday morning -- two days after the killing.

The suspect was "positively identified from the CCTV footage at the airport and was alone at the time of arrest," Khalid said in a statement.

Meanwhile, pathologists in the Malaysian capital examined the body for clues as to how he died, in a killing that has echoes of Soviet-era spycraft.

If confirmed, the assassination, which analysts said could have been ordered over reports he was readying to defect, would be the highest-profile death on Kim Jong-Un's watch since the 2013 execution of his uncle, Jang Song-Thaek, in a country with a long record of meting out brutal deaths.

- Seizure -

South Korea's spy chief Lee Byung-Ho said the two women struck on Monday morning as Kim was readying to board a flight to Macau where he has spent many years in exile.

Malaysian police said Kim, a portly 45-year-old, was walking through the departure hall when he was attacked.

"He told the receptionist... someone had grabbed his face from behind and splashed some liquid on him," Selangor state's criminal investigation chief Fadzil Ahmat was reported as saying by Malaysia's The Star newspaper.

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"He asked for help and was immediately sent to the airport’s clinic. At this point, he was experiencing headache and was on the verge of passing out,” said Fadzil.

"At the clinic, the victim experienced a mild seizure. He was put into an ambulance and was being taken to the Putrajaya Hospital when he was pronounced dead."

An autopsy at Kuala Lumpur Hospital's forensics department was completed by Wednesday evening, Selangor Police Chief Abdul Samah Mat told AFP, but said no results had yet been issued by the hospital.

A black Jaguar sedan bearing the North Korean flag was seen outside the department, and four officials wearing flag pins were observed within the forensics compound.

The officials left the department around 8pm (1200 GMT) without commenting to reporters.

No party had yet laid claim to the body, Abdul Samah said.

"As for now the body will be kept at the Kuala Lumpur morgue."

- Fall from grace -

Kim, 45, had at one time been set to assume the leadership of his isolated country, but fell out of favour after an embarrassing attempt to get into Japan on a fake passport in 2001.

Kim has since lived in exile, gaining a reputation as something of a playboy with much of his time spent in the gambling enclave of Macau, where he was believed to have enjoyed some protection from Chinese security forces.

Quizzed about the killing during a regular press conference, Chinese foreign ministry spokesman Geng Shuang said Beijing was aware of the reports.

"According to our understanding, the incident took place in Malaysia and the Malaysian side is investigating this issue. We are following the developments," he said.

In Pyongyang, celebrations were under way for Thursday's anniversary of the birth of Kim Jong-Il, Jong-Nam's father, with an ice-skating gala that made no mention of the drama.

Jong-Un has been trying to strengthen his grip on power in the face of growing international pressure over his country's nuclear and missile programmes, and regular reports have emerged on purges and executions.

Jong-Nam, known as an advocate of reform in the North, once told Japanese reporters that he opposed his country's dynastic system.

In a 2012 interview from his school in Bosnia, a 17-year-old Kim Han-Sol, Jong-Nam's son, said his father had been passed over for succession because he "was not really interested in politics".

"I don't really know why he became a dictator," Kim said of his uncle Kim Jong-Un. "It was between him and my grandfather."

It emerged Wednesday that Jong-Nam had pleaded with his younger brother for his life to be spared after an earlier assassination attempt.

"Jong-Nam in April 2012 sent a letter to Jong-Un saying 'Please spare me and my family,'" Kim Byung-Kee, a member of South Korea's parliamentary intelligence committee, told reporters.

Cheong Seong-Chang of the independent Sejong Institute in Seoul said the assassination was "unthinkable without a direct order or approval from Kim Jong-Un himself".

His killing was likely motivated by a recent news report that Kim Jong-Nam had sought to defect to the EU, the US or South Korea as far back as in 2012, he said.