North Korean foreign and national security ministries plotted the murder of Kim Jong-nam, South Korea's intelligence agency reportedly told lawmakers in Seoul.

"The assassination of Kim Jong-nam was an act of systematic terror ordered by Kim Jong-un," South Korean lawmaker Kim Byung-kee said in a televised address, as reported by CNN.

"The operation was conducted with two assassination groups and one supporting group," Byung-kee reportedly said.

The lawmakers were told that the ministries recruited the two female suspects to kill Jong-nam.

Police said Jong-nam, the half-brother of North Korean leader Jong-un, was killed at KLIA2 on Feb 13.

North Korea had repeatedly denied its hand in the death and cast doubts on Malaysian investigations.

Yesterday, Health Minister Dr S Subramaniam said the post-mortem revealed Jong-nam died of organophosphate poisoning with the substance found in his system matching the characteristics of nerve agent VX.

Jong-nam likely died a painful death within 15 to 20 minutes of exposure to the substance, he said.

Leaked CCTV footage showed two women approaching Jong-nam, before he sought help from KLIA2 personnel who took him to the clinic.

Subramaniam said to Jong-nam fainted at the clinic and died in an ambulance en route to the hospital.

Police have arrested two women who held Vietnamese and Indonesian passports.

The women reportedly said they believed they were part of a prank.

Indonesian consular officers who visited one of the suspects to determine if she was indeed an Indonesian citizen, were told that she thought the substance was baby oil.

Inspector-general of police Khalid Abu Bakar said the woman had vomitted in the taxi on the way back from the airport, believed to have been caused by the substance.

He dismissed claims that the suspects thought they were recording a prank video, adding that they had administered the poison onto Jong-nam's face using their bare hands.

They were told to wash their hands immediately, he said.

In the leaked CCTV footage, the Vietnamese suspect was seen walking calmly away from Jong-nam within seconds of approaching him.

Police are seeking four North Korean men, and three others whose nationalities have yet to be determined, in relation to the case.