A preliminary report shows the murder of Kim Jong-nam was carried out with a highly toxic chemical known as VX nerve agent, Malaysian police say.

The police said swabs were taken from the eye and the face of a North Korean national by the Chemistry Department of Malaysia.

What is VX gas? A highly toxic and rapidly acting chemical warfare agent developed in the UK in the 1950s

A highly toxic and rapidly acting chemical warfare agent developed in the UK in the 1950s The most potent of all nerve agents, it is much more potent than the well-known sarin but works in a similar way

The most potent of all nerve agents, it is much more potent than the well-known sarin but works in a similar way Symptoms appear within seconds of exposure to the vapour or after exposure to the liquid form

Symptoms appear within seconds of exposure to the vapour or after exposure to the liquid form A large dose of VX may result in convulsions, loss of consciousness, paralysis and respiratory failure possibly leading to death

A large dose of VX may result in convulsions, loss of consciousness, paralysis and respiratory failure possibly leading to death It is possible that any visible VX liquid contact on the skin, unless washed off immediately, would be lethal

It is possible that any visible VX liquid contact on the skin, unless washed off immediately, would be lethal Only one person has ever been officially confirmed as having died from VX *Source: Centres for Disease Control and Prevention

A statement from the inspector general of police said a preliminary analysis from the department identified the substance as VX nerve agent, or S-2 Diisoprophylaminoethyl methylphosphonothiolate, a chemical classified as a weapon of mass destruction by the United Nations.

"Other exhibits are under analysis," Malaysian police chief Khalid Abu Bakar said in the statement.

Mr Khalid said earlier that a Vietnamese woman and an Indonesian woman wiped a liquid on Kim's face — they later washed their hands and fled the scene.

But he said one of them had suffered from the effects of the chemical and had been vomiting.

Airport camera footage released on Monday by Japanese broadcaster Fuji TV shows the moment the women appeared to assault Kim, who is later seen asking airport officials for medical help. He died on the way to hospital.

VX is tasteless and odourless, and is outlawed under the Chemical Weapons Convention, except for "research, medical or pharmaceutical purposes".

It can be manufactured as a liquid, cream or aerosol. Absorbed in large doses, it is fatal after 15 minutes, according to the US Army's Edgewood Chemical Biological Centre, making it the most toxic known nerve agent in the world.

Kim, the estranged half-brother of North Korean leader Kim Jong-un, died on February 13 after two women put a substance on his face while he was checking in at Kuala Lumpur International Airport while he was preparing to board a flight to Macau.

Police chief Khalid said help had been sought from Interpol to issue an alert for the four North Korean suspects who left Malaysia on the same day Kim was killed.

It was unclear what Interpol could do, as the four are believed to have returned to Pyongyang and North Korea is not a member of Interpol.

Mr Khalid said there were no plans to send officers to Macau to collect a DNA sample from Kim's family.

Kim had a home in Macau and was on his way there when he was killed.

North Korea says Malaysia has 'complicated' investigation

North Korea said Malaysia's investigation into the death of one of its nationals was full of "holes and contradictions" amid speculation its agents masterminded the assassination.

Malaysian police have not directly pinpointed North Korea as being behind the death of Kim.

The Korean Jurists Committee said in a statement on state-run news agency KCNA that the Malaysian investigation lacked fairness and has been influenced by the South Korean Government, which blames Pyongyang for the death.

The North has not acknowledged that the dead man is Kim.

Thursday's statement described the man only as a North Korean citizen bearing a diplomatic passport.

Reuters/AP