Mr Kim died last week after two women wiped a substance over his face in a check-in hall at Kuala Lumpur airport.
Malaysian toxicology reports have identified the chemical as "VX nerve agent", classified as a weapon of mass destruction by the United Nations.
Malaysia has not blamed the North Korean state for the death, but says North Koreans were clearly behind it.
Mr Kim died on the way to hospital shortly after the 13 February airport encounter. His body remains in a hospital mortuary, amid a diplomatic dispute over who should claim it.
North Korea responded furiously to Malaysia's insistence on conducting a post-mortem examination and has accused Malaysia of having "sinister" purposes.