Kim Jong-nam VX gas murder puts North Korea's 5,000-tonne chemical WMD stockpile in the spotlight

North Korea is one of only four countries worldwide that is not a signatory to the International Chemical Weapons Convention (CWC) and is thought to have had a weapons programme that dates back to the 1980s. But unlike its regular nuclear tests, Pyongyang has not flaunted its chemical weapons capability – until now.

The assassination of Kim Jong-nam, the half-brother of North Korea's leader Kim Jong-un, in Kuala Lumpur airport last week demonstrated that the country had mastered the use of VX agents – known as nerve gas – which Malaysian officials have claimed was found on the 45-year-old's mouth and face.

South Korea claims that in addition to VX, its northern neighbour has 25 other types of nuclear chemical agents, including sarin, mustard gas and hydrogen cyanide. Seoul believes that Pyongyang has amassed as much as 5,000 tonnes of chemical weapons and is capable of deploying them in missiles or via artillery fire over the border at South Korean troops.

Meanwhile, the Nuclear Threat Initiative puts North Korea's chemical agent production capability at 4,500 metric tonnes during a typical year, and as much as 12,000 tonnes per year during a period of crisis. Its current inventory is thought to be between 2,500 to 5,000 tonnes.

VX was used by former Iraqi dictator Saddam Hussein in his 1988 attack on the Kurdish city of Halabja, which killed up to 5,000 people. If North Korea did deploy it in the King Jong-nam assassination, it would suggest a new level of sophistication in its handling of chemical weapons, Associated Press reported.

"They probably conducted a lot of tests to come up with a perfect amount that would kill Kim Jong Nam, but not harm the assailants or anyone else nearby in a crowded airport," Kim Dae Young, a military expert at South Korea's Korea Defense and Security Forum, said.

Making VX is not that difficult, and it is thought that Pyongyang would have used chemical fertiliser plants to manufacture them. But Kim also told AP that the weapon only has a short lifespan. "The biggest weakness of chemical weapons is that their effectiveness expires soon and new supplies need to be made constantly," he said

In February 2014 the United Nations Human Rights Council reported that North Korea had possibly tested weapons on prisoners and the disabled, but that testimony could not be confirmed. It is claimed that the country has concentrated on acquiring mustard gas, phosgene, sarin and v-type chemical agents.

Since its discovery, VX agents have been researched, produced and stockpiled by several countries, but most have now given up their offensive chemical weapons programmes and are in the process of destroying their stockpiles. This process is overseen by the Organisation for the Prohibition of Chemical Weapons (OPCW).