The United States on Tuesday said North Korea had used the banned chemical nerve agent VX to assassinate Kim Jong-un’s half brother Kim Jong-nam in Malaysia in 2017. The American investigators had reached the conclusion on February 22.

“The United States strongly condemns the use of chemical weapons to conduct an assassination,” State Department Spokesperson Heather Nauert said. “This public display of contempt for universal norms against chemical weapons use further demonstrates reckless nature of North Korea and underscores [that] we cannot afford to tolerate a North Korean WMD [weapons of mass destruction] programme of any kind.”

The US statement comes hours after Pyongyang promised it would not use nuclear or conventional weapons against the South, and said it was ready for denuclearisation if military threats to the country were removed.

Two women are on trial for killing Kim Jong-nam. Four men, suspected to be North Korean agents, are suspected to have orchestrated the assassination. They allegedly got the two women – Indonesian Siti Aisyah and Doan Thi Huong from Vietnam – to smear Kim Jong-nam with VX at a terminal of the Kuala Lumpur airport, leading to his death within minutes.

The women, who were arrested a few days after the assassination and face death by hanging if convicted, have pleaded not guilty. They maintain that they were tricked into believing they were taking part in a prank for a reality television show.