Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, died after being attacked with the highly toxic nerve agent VX at Kuala Lumpur International Airport, Malaysian authorities said. The killing has prompted an investigation, public safety concerns and a diplomatic dispute between Malaysia and North Korea.

On February 13, two women approached Kim in the airport check-in hall and wiped a substance on his face as he waited for a flight to Macau, where he lived with his family. He sought help from airport staff, suffered convulsions and died on the way to hospital. Preliminary toxicology tests detected VX in swabs from his eyes and face. One of the women later suffered vomiting, police said.

Malaysian investigators suspect North Korean agents directed the attack. Authorities detained the two women, one Vietnamese and one Indonesian, and sought several North Koreans, including an embassy official and an employee of the state airline. Relatives and acquaintances of the women said they may have been tricked; Malaysian police maintained that the women knew they were handling a toxin, pointing to their washing their hands after the attack. Investigators were also trying to determine how VX entered Malaysia.

North Korea denied responsibility, criticised Malaysia’s investigation and post-mortem examination, and blamed Malaysia for the death. It did not acknowledge that the dead man was Kim Jong-nam, identifying him only as a North Korean citizen; his passport bore the name Kim Chol. Malaysia warned that it could expel the North Korean ambassador over his accusations.

VX is an odourless, oily nerve agent that can kill in minute quantities through skin contact. It is banned under the Chemical Weapons Convention, which North Korea has not signed. Experts questioned how the attackers handled the substance and raised concerns that it could persist on surfaces. Malaysian authorities began decontaminating areas of the airport after the finding; no passengers, airport workers or medical personnel were reported ill.

Kim Jong-nam was the eldest son of former North Korean leader Kim Jong-il and was once seen as a possible successor. He lived abroad for years and became a critic of the country’s leadership and dynastic succession. North Korea is widely believed to possess a large chemical weapons stockpile, including VX, and to have substantial production capacity.