KUALA LUMPUR - The two women accused of smearing poison on the face of the estranged half-brother of North Korean leader Kim Jong Un at Kuala Lumpur International Airport last week knew that they were dealing with poison and had rehearsed the attack, said Malaysian police.

Dismissing reports that the duo were duped into playing a prank on Mr Kim Jong Nam, Inspector General Khalid Abu Bakar told a press conference that the women had practised the attack in two downtown malls before executing it at the airport on Feb 13.

"We strongly believe it is a planned thing and they have been trained to do that. It is not something like just shooting a movie or a play thing," he said.

He said that the two women were given the liquid by four North Korean men, who have since fled to Pyongyang. The Indonesian woman, Siti Aisyah, 25, attacked first, followed by the Vietnamese woman, Doan Thi Huong, 28.

Confirming that leaked CCTV footage from the airport was real, the police chief added that the footage showed one of the women moving away after the attack, with her hands held up away from her body, "towards the washroom".

"So she knew very well that it is toxic and she has to wash her hands," he said.

After the attack, Mr Kim, 46, told airport staff that he felt unwell. He died on the way to the hospital.

The two women, who were picked up last week, have had their remand orders extended for another week. Police have also remanded a North Korean man, Ri Jong Chol, 46, who has been in Malaysia on a work visa since 2013. A fourth suspect, the Malaysian boyfriend of Siti Aisyah's, Muhammad Farid Jalaluddin, 26, will be released on police bond.