North Korea killed Kim Jong-un's brother with VX agent

North Korea ordered the assassination of Kim Jong-un's brother with a banned chemical agent in Kuala Lumpur airport, the US State Department has found.

State Department spokeswoman Heather Nauert said in a statement that US investigators operating under the 1991 Chemical and Biological Weapons Control and Warfare Elimination Act had determined on February 22 that North Korea was to blame for the murder and that VX was used.

"This public display of contempt for universal norms against chemical weapons use further demonstrates the reckless nature of North Korea and underscores that we cannot afford to tolerate a North Korean WMD program of any kind," Ms Nauert said.

Doan Thi Huong of Vietnam (L) and Siti Ashyah of Indonesia (R), were charged with the murder of Kim Jong-Nam, the half brother of North Korean leader Kim Jong-Un. Photos / AP

The finding was formally published on today and immediately triggered another layer of US economic sanctions against Pyongyang, just as South Korea reported that the regime is ready for talks to end a nuclear standoff.

Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, died after two women approached him and smeared the deadly nerve agent on his face in Malaysia on February 13 last year.

Multiple witnesses watched on in horror as Jong-Nam struggled to breathe. Then his eyes rolled back before he lost consciousness. In little more than an hour, he was dead.

The late Kim Jong-Nam and current North Korean leader Kim Jong-un, were estranged brothers. Photos / AP

Sweat streamed from his face as he approached an airport information counter to report the assault. Juliana Idris was the first person he spoke to at the counter.

"His hands were shaking a bit," she said.

He told her he'd been "attacked from behind by two women," with one of them wiping something over his eyes.

Idris was one of a number of witnesses to recount the Kim Jong-nam's final moments as the trial began in Malaysia of two women accused of brazenly assassinating him on February 13 by smearing an exotic poison on his face.

Kim Jong-Nam slumped in a chair at Kuala Lumpur International Airport. Photo / NST

Site Aisyah of Indonesia and Doan Thi Huong of Vietnam have been charged with murder using the banned VX nerve agent.

Kim Jong-Namhad once been seen as his father Kim Jong-Il's natural heir, and some reports had suggested that China might be grooming him to replace the younger man in the event of a crisis.