A female assassin who murdered Kim Jong-un's half-brother used the world's deadliest chemical weapon that needs just a drop to kill someone, it has emerged.

Kim Jong Nam, 45, had traces of VX, which is classified as a weapon of mass destruction by the United Nations, on his face and his eyes after being targeted at Kuala Lumpur International Airport.

Experts say only a minute amount of the banned nerve agent is needed to kill.

North Korean dictator Kim Jong-un is believed to have a large stockpile of the poison among a terrifying arsenal of up to 5,000-tonnes of chemical weapons.

It comes as a new image emerged of Doan Thi Huong, the Vietnamese woman who was arrested by Malaysian police over the murder, posing for photos in a white bikini during a motor show in Hanoi.

Scroll down for video

Shocking pictures show Kim Jong-Nam slumped in a chair having been poisoned

Vietnamese woman Doan Thi Huong, who was arrested by Malaysian police over the murder of Kim Jong Nam, poses for a photo during a motor show in Hanoi, Vietnam in July

Kim Jong Nam died on February 13 and now police say a nerve agent was found on his face

The nerve agent VX, which has the consistency of motor oil, can take days or even weeks to evaporate

Reports of the use of a nerve agent raised serious questions about public safety in Kuala Lumpur International Airport that authorities went 11 days without decontaminating.

If VX was used, it could have contaminated not only the airport but anywhere else Jong Nam had been, including medical facilities and the ambulance he was transported in. The nerve agent, which has the consistency of motor oil, can take days or even weeks to evaporate.

Security experts say it would be easy to smuggle a small amount of VX into Malaysia in a diplomatic pouch, which are not subject to regular customs checks.

Police said one of two women suspected of the killing was vomiting profusely afterwards and experts says that his murderers were probably wearing thin gloves and washed their hands afterwards to avoid killing themselves.

The revelation raised serious questions about public safety in a building that authorities went 11 days without decontaminating.

If VX was used, it could have contaminated not only the airport but anywhere else Jong Nam had been, including medical facilities and the ambulance he was transported in. The nerve agent, which has the consistency of motor oil, can take days or even weeks to evaporate.

Security experts say it would be easy to smuggle a small amount of VX into Malaysia in a diplomatic pouch, which are not subject to regular customs checks.

VX, THE LETHAL TOXIN CREATED BY BRITAIN VX is the deadliest nerve agent ever created, and is classed as a weapon of mass destruction by the UN. Just a fraction of a drop, absorbed through the skin, can take effect within seconds and fatally disrupt the nervous system. It is the only nerve agent to have been created since the Second World War, having been synthesised in Britain in the early 1950s. A liquid at room temperature, it has a similar consistency to motor oil, and evaporates as slowly. Inhaled as a vapour it is ten times more lethal than a liquid, causing poisoning symptoms within seconds, blurring the victim’s vision and leaving them coughing and fighting for breath. Experts say it is like drowning on dry land. Similar to a pesticide, it works by preventing the proper operation of an enzyme which acts as the body’s ‘off switch’ for muscles and glands, acetylcholinesterase. Without that switch, they are constantly stimulated and rapidly tire. The victim dies when the muscles in their diaphragm fail and they can no longer breathe. The agent is thought to have been used in chemical warfare during the Iran-Iraq War in the 1980s. It is up to 150 times more deadly than sarin, the nerve gas released by a Japanese doomsday cult on to the Tokyo subway in 1995. The V in VX stands for ‘venom’, in tribute to its high toxicity and how rapidly it penetrates the skin, even through clothing. However, there is an antidote – a chemical called atropine sulphate, which helps people breathe by drying bronchial secretions and opening airways. The antidote is carried routinely by members of the US military. A drop of VX the weight of a pound coin contains 950 human lethal doses. Advertisement

Police said one of two women suspected of the killing was vomiting profusely afterwards and experts says that his murderers were probably wearing thin gloves and washed their hands afterwards to avoid killing themselves.

VX and Sarin was used by a Japanese religious cult who killed a dozen commuters on Tokyo's underground rail network in 1995. Saddam Hussein was accused of using it on Kurds in the 1980s and Bashar al-Assad's regime in Syria had stockpiled huge amounts before it was taken away in 2014.

CCTV footage of Jong-Nam's final minutes shows one female assassin wiping a fast-acting poison on his face from behind.

Other shots show him stumbling, wiping his face, and seeking help from people while gesturing to his eyes before being escorted to a clinic. He later slumped in a chair after he suffered a seizure and died on February 13.

Traces of VX, considered one of the five most deadly chemical weapons of war that produces a feeling of drowning before death, were detected on swabs of the dead man's face and eyes.

Matthew Meselson, a professor of biochemistry at Harvard, told the Washington Post that VX is quite easy to produce.

The board member of the Center for Arms Control and Non-Proliferation said: 'A good organic chemist could synthesize VX relatively easily. You could get the ingredients and make it in a couple of days, and if you make it pure, it's quite stable'.

Police have not said how the women were able to apply the nerve agent to his face and also avoid becoming ill themselves.

Detectives said earlier that the two attackers rubbed a liquid on Kim Jong Nam's face before walking away and quickly washing their hands. He sought help from airport staff but died before he reached the hospital.

NORTH KOREA'S 5,000-TONNE STASH OF CHEMICAL WEAPONS North Korea has up to 5,000 tonnes of chemical weapons, South Korean experts said today, including the toxin used to assassinate its leader's half-brother. Traces of VX - a nerve agent listed as a weapon of mass destruction by the United Nations - were detected on swabs from the face and eyes of Kim Jong-Nam. South Korea's defence ministry said in its 2014 Defence White Paper that the North began producing chemical weapons in the 1980s and estimated that it has about 2,500 to 5,000 tonnes in stock. North Korea has chemical weapons production facilities in eight locations including the northeastern port of Chongjin and the northwestern city of Sinuiju, it said in the 2012 edition of the document. North Korea has up to 5,000 tonnes of chemical weapons, South Korean experts said today, including the toxin used to assassinate its leader's half-brother 'North Korea is believed to have a large stockpile of VX, which can easily be manufactured at low cost,' defence analyst Lee Il-Woo at the private Korea Defence Network told AFP. Military science professor Kim Jong-Ha at Hannam University said the North has 16 kinds of nerve agents including VX and sarin, used by a Japanese doomsday cult, Aum Shinrikyo, in the 1995 attack at the Tokyo subway system that killed 12 people. It also possesses other lethal chemicals, including suffocating, blistering and blood agents, Kim said, as well as 13 types of biological weapons such as anthrax and bubonic plague. North Korea has not signed a global chemical weapons convention that prohibits the production, stockpiling and use of chemical weapons. More than 160 countries signed the treaty, that went into force in 1997. Advertisement

VX nerve agent, or S-2 Diisoprophylaminoethyl methylphosphonothiolate, is chemical weapon classified as a weapon of mass destruction by the United Nations.

The seeming contradiction of a poison that could kill him quickly but not sicken the attackers has stumped outside experts.

Bruce Goldberger, a leading toxicologist who heads the forensic medicine division at the University of Florida, said some protective measures must have been in place if the women handled the substance without gloves.

'It's also possible that the toxin was encapsulated, then activated when applied to the skin,' he said before the latest police statement. 'As additional information is provided to the media by the police, it seems more likely that a new or modified chemical or biological agent was utilized in the attack.'

Alleged aassasin Doan Thi Huong had a Facebook account under the name Ruby Ruby and posted pictures of herself wearing a revealing red swim suit

Suspected assassin Doan Thi Huong can be seen wearing a shirt with 'LOL' emblazoned on the front

'The other chemical agents like sarin, tabun, those kinds of things, they're way below this. They're toxic, yes, but this is the king,' said John Trestrail, a U.S. forensic toxicologist who has examined more than 1,000 poisoning crimes.

He said an amount of VX weighing two pennies could kill 500 people though skin exposure.

He and other experts stressed the importance of having the results confirmed by an independent reference laboratory, especially given the nerve agent's rarity.

But South Korea said today that the use of VX was a 'blatant violation' of an international treaty.

'We are shocked by the latest revelation by the Malaysian authorities that VX... was used in the death of Kim Jong-Nam,' Seoul's foreign ministry said in a statement.

It called it a 'blatant violation of the Chemical Weapons Convention and other international norms'.

Unlike Pyongyang, Seoul - which first pointed the finger at the North over Kim's death - is a signatory to the Convention, which went into force in 1997.

'The use of any chemical weapons is strictly banned for any reason and in any place,' the foreign ministry statement said.

A similar white top was worn by a woman shown in CCTV footage from the terminal minutes after Kim Jong-nam was killed

South Korea's defence ministry said in its 2014 Defence White Paper that the North began producing chemical weapons in the 1980s and estimated that it has about 2,500 to 5,000 tonnes in stock.

In a 2015 assessment, the Washington-based Nuclear Threat Initiative wrote: 'North Korea claims that it does not possess chemical weapons.

'While assessing stockpiles and capabilities are difficult, the DPRK is thought to be among the world's largest possessors of chemical weapons, ranking third after the United States and Russia.'

Malaysia's police chief said last night that investigators want to question a North Korean embassy official about Kim Jong Nam's death, saying he should cooperate if he has nothing to hide despite having diplomatic immunity.

North Korea has previously used diplomatic pouches 'to smuggle items including contraband and items that would be subjected to scrutiny if regular travel channels were used', said Rohan Gunaratna, the head of the Singapore-based International Centre for Political Violence and Terrorism Research.

Inspector-General of Police Khalid Abu Bakar has previously said the woman who ambushed Kim from behind clearly knew she was carrying out a poison attack, dismissing claims that she thought she was taking part in a TV prank.

'The lady was moving away with her hands towards the bathroom,' Khalid said earlier this week.

HOW A SINGLE DROP OF MAN-MADE VX KILLS IN MINUTES As Malaysian toxicologists reveal that the banned nerve agent VX was used in the airport assassination of Kim Jong-Nam, here are some key questions and answers about the deadly weapon of mass destruction. What is it? Code-named by the US scientists who mass produced it, VX is an organophosphate compound and one of the deadliest chemical agents ever manufactured. Stockpiled by the US in huge quantities during the Cold War, VX is perhaps 10 times as powerful as the Sarin toxin. Odourless and clear when pure, it has the appearance of motor oil and is stable enough to be transported. It is also hard to detect, an advantage for a would-be assassin. Downsides are that it lingers, potentially contaminating areas for long periods of time. 'It can kill an adult weighing 70 kilogrammes with just five milligrammes on the skin,' said Yosuke Yamasato, former principal of the Japan Ground Self-Defense Force Chemical School. 'It's unbelievable that the executors of the crime used it with their bare hands - they must have not known the material was VX.' Code-named by the US scientists who mass produced it, VX is an organophosphate compound and one of the deadliest chemical agents ever manufactured (file picture) What does it do? It strikes the nervous system fast. A high dose can kill in minutes when inhaled, as the blood vessels in the lungs rapidly spread the compound into the bloodstream and vital organs. Nerve agents over-stimulate glands and muscles, leading them to quickly fatigue and become unable to sustain breathing. Symptoms depend on dosage and whether it is inhaled or introduced through the skin - the slower form of poisoning. Exposure to low doses is survivable. But more serious contamination is fast-acting and often gruesome. People exposed to the toxin may become short of breath and nauseous in minutes, or at a higher dose experience seizures, heart failure and a total shut down of the respiratory system. There are antidotes but treatment must be immediate. US soldiers carried kits to inject themselves with antidote during the first Iraq War. Nerve agent VX is odorless, tasteless and highly toxic, and is manufactured for chemical warfare Where does it come from? The compound was first created in a British laboratory in the early 1950s. But American scientists honed its potency during the Cold War arms race with the Soviet Union. Tens of thousands of tonnes of VX were churned out at Newport Chemical Depot in Indiana - a stockpile that was finally destroyed in the late 1980s as the Cold War ended. Accidental leaks have been reported in the US and Japan. It has been deployed as a war weapon infrequently but with devastating effect. Residues found on site suggest Iraqi dictator Saddam Hussein may have used VX among a cocktail of chemical weapons he rained down on the Kurdish town of Halabja in 1988 killing at least 5,000 people. In 1994 VX was used by Japan's Aum cult to murder an office worker in Osaka, and in the attempted murder of two other people. Legal status? VX is listed a weapon of mass destruction by the United Nations. Under the international Chemical Weapons Convention 1997, countries are allowed limited stockpiles for research purposes only but must declare them and are obliged to progressively destroy their supplies. 'North Korea is not a signatory to CWC, so it's no surprise if it possesses VX,' Satoshi Numazawa, professor of toxicology at Showa University, told AFP. Advertisement

'She was very aware that it was toxic and that she needed to wash her hands.'

The leaked CCTV footage shows Kim asking for help from airport staff, who direct him to a clinic, after he is ambushed.

Police said he suffered a seizure and died before he reached hospital.

Detectives are holding three people - women from Indonesia and Vietnam, and a North Korean man - but want to speak to seven others, four of whom are believed to have fled to Pyongyang.

One man wanted for questioning, who is believed to be still in Malaysia, is senior North Korean embassy official Hyon Kwang Song.

Police have acknowledged that his diplomatic status prevents them from questioning him unless he surrenders himself.

However, a North Korean official outside Pyongyang's Kuala Lumpur embassy said Friday Malaysia had not submitted a request to speak to Hyon, despite the police chief earlier saying the embassy would be asked for assistance.

Khalid said police have also asked Interpol to issue an alert for four North Korean men who left Malaysia the same day Kim Jong Nam was attacked by the two women.

The four men are believed to be back in North Korea, but police also want to question three other people still in Malaysia, including Hyon Kwang Song, a second secretary at the North Korean Embassy.

Malaysian police said two women allegedly involved in the assassination - Siti Aisyah (left) and Doan Thi Huong (right) - knew the poisoning wasn't a 'TV prank'

Police want to question the North Korean embassy's second secretary, Hyon Kwang Song (left), as well as a North Korean airline employee called Kim Uk Il (right)

North Korean Ri Ji U has also been identified for questioning in connection with the murder of Kim Jong Nam

'The foreign officer has got immunity so we have to follow protocol,' Khalid told reporters. 'If you have nothing to hide, you don't have to be afraid. You should cooperate.'

Khalid acknowledged that Malaysia would not be able to question Hyon if the embassy exercises its immunity privileges.

North Korea's official, state-controlled media mentioned the case for the first time Thursday, saying Malaysia's investigation was full of 'holes and contradictions' without acknowledging the victim was Kim Jong Nam.

The report from KCNA largely echoed past comments by North Korea's ambassador to Malaysia, but the publication of at least some news inside North Korea could be a sign of its concern over growing international speculation that Pyongyang dispatched a hit squad to kill Kim Jong Nam.

HOW JAPANESE CULT ALSO USED DEADLY NERVE AGENT A Japanese religious cult that carried out a deadly nerve gas attack on Tokyo's subways in 1995 also experimented with the VX nerve agent suspected in the killing of North Korean leader Kim Jong Un's half brother in Malaysia. Months before killing about a dozen commuters and severely injuring dozens more in Tokyo with sarin, another kind of nerve gas, in March 1995, the Aum Shinrikyo cult tried VX on at least three victims, killing one whom cult members believed was a police informant. In their trial, cult members said they practiced using syringes to spray the deadly chemical on people's necks as they pretended to be out jogging. The suspected police informant spent 10 days in a coma before dying. One of the people attacked with VX by the cult, Hiroyuki Nagaoka, told Japanese public broadcaster NHK on Friday that news of Kim Jong Nam's murder reminded him of his own experience. A Japanese religious cult - led by Shoko Asahara (centre) - that carried out a deadly nerve gas attack on Tokyo's subways in 1995 also experimented with the VX nerve agent suspected in the killing of North Korean leader Kim Jong Un's half brother He was walking on the sidewalk in his neighborhood in Tokyo in January 1995 when a member of the cult sprayed the nerve agent on the back of his neck. Most of it was blocked by his jacket collar. 'I had no idea what happened at that time,' he said. He was attacked because he was a vocal opponent of the cult. He finished walking home but about half an hour later realized everything seemed to be oddly dark - an effect of the toxin causing his pupils to shrink. He started feeling hot inside and, sweating profusely, took off his clothes. His wife later told him that he got down on all fours like an animal, twisting and scratching his neck and chest, before rolling onto his back in pain and losing consciousness. He was rushed to a hospital for emergency treatment, and was unconscious for several days. 'I was saved by the collar of the jacket I was wearing,' he told NHK after officials in Malaysia said they suspected VX in the Kuala Lumpur killing. He still has numbness on the right side of his body and uses an oxygen tube inserted in his nostrils to assist his breathing. Nagaoka said when he saw Kim Jong Nam in an airport surveillance video walking unassisted for a while but gradually seeming to slow down, he thought it must be VX. He also said Kim might have been sweating heavily like he did, citing wet spots on Kim's shirt when he was shown slumped in a chair. Advertisement

Long estranged from North Korea's leadership, Kim Jong Nam had lived outside the country for years, staying in Macau, Singapore and Malaysia.

The two suspected attackers, an Indonesian woman and a Vietnamese woman, are in custody.

Doan Thi Huong, 28, is one of the women being held in Malaysia over the killing of Kim Jong-nam. She posted a Facebook selfie online just days before the assassination and can be seen wearing a shirt with 'LOL' emblazoned on the front.

A similar white top was worn by a woman shown in CCTV footage from the terminal minutes after Kim Jong-nam was killed.

Separate photos, in a Facebook account under the name of Ruby Ruby, show her posing in a revealing red swim suit and wearing a black dress with floral patterns.

Jong-Nam died on February 13 after being attacked as he waited for a plane to Macau