KUALA LUMPUR (Reuters) - VX, the chemical used in the airport murder of Kim Jong Nam, is one of the deadliest chemical weapons created by man. Just 10 milligrams of the nerve agent or a single drop is enough to kill in minutes, experts say.

With the texture and feel of engine oil, VX was first produced in the United Kingdom in the 1950s. It can cause convulsions, loss of consciousness, paralysis and respiratory failure in minutes.

Its only known use is as a chemical warfare agent: VX is classified as a weapon of mass destruction by the United Nations.

"You can think of VX as being a pesticide on steroids, this is an extraordinarily toxic substance," said Bruce Bennett, a specialist in North East Asian security issues at the California-based RAND Corp. "Roughly 1/100th of a gram, a third of a drop, on someone's skin, will kill them."

Malaysian police said on Friday that VX was found on the body of Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong UN.

Police said they were investigating whether the VX was brought into the country - and how that was done - or concocted inside the country.

VX and other nerve agents were believed to have been used in chemical warfare during the Iran-Iraq War in the 1980s.

Sarin gas was used in Syria, killing hundreds in deadly attacks in 2013, while a mix of Sarin and VX was used by members of a Japanese doomsday cult in their deadly 1995 attack on a Tokyo subway.

THIRD-LARGEST STOCKPILE

North Korea is believed to have the world's third-largest stockpile of chemical weapons, according to the Nuclear Threat Initiative project, which analyses weapons of mass destruction.

North Korea is one of only six countries in the world that have not signed a global chemical weapons convention that prohibits the production, stockpiling and use of chemical weapons.

Pyongyang has denied it has chemical weapons.

South Korean defence officials have estimated that Pyongyang has between 2,500 and 5,000 tonnes of chemical weapons in stockpiles.

South Korean analysts have identified Sarin and VX as the focus of a North Korean chemical weapons programme.

But VX is known to be much more potent than Sarin and other nerve agents because of its persistency. Sarin evaporates from the skin surface but VX does not.

The chemical is hard to produce but a few countries are known to make it and remain in possession of it. The United States and Russia still have some VX stockpiles.

AIRPORT SECURITY

VX is toxic through skin contact but much more lethal in gaseous form.

Symptoms after contact with VX in vapour form will appear within a few seconds, and within a few minutes to up to 18 hours after exposure to the liquid form, said John Allum of forensic science firm Hawkins.

People may not even know they have been exposed to VX as it is tasteless and odourless. In fact, it is unlikely to have been detected by airport security or sensors if it had been brought in small amounts.

VX can be transported in sealed containers, without affecting the person holding the chemical, experts say.

It is also possible to survive some exposure to VX, if immediate medical attention is provided or if it is washed off quickly.

Malaysian police say two women are believed to have attacked Kim Jong Nam, using their bare hands to wipe his face with a liquid. The women were then instructed to wash their hands off afterwards.

North Korea unsuccessfully tried to prevent an autopsy on the body, accusing Malaysia of working with South Korean and other "hostile forces." Pyongyang has said Malaysia should be held responsible for killing one of its citizens, though it has not acknowledged the victim is Kim Jong Un's half-brother.

The two women and a North Korean have been detained in Kuala Lumpur. Police are searching for seven other North Koreans, four of whom are believed to have fled to Pyongyang.

(Additional reporting by Greg Torode in Hong Kong and Emily Chow in Kuala Lumpur; Editing by Praveen Menon and Bill Tarrant)