The Organisation for the Prohibition of Chemical Weapons (OPCW) said its executive council "unequivocally condemned the use of any chemical weapon by anyone under any circumstances."
The council, made up from 40 member states, called "for those responsible for the use of chemical weapons to be held accountable."
It also asked the OPCW's director general Ahmet Uzumcu to "provide technical assistance upon request from Malaysian authorities for its national investigation."
"The council underscored its deep interest in receiving and considering the official results of the investigation" once completed by Malaysia.
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Malaysian authorities had earlier declined to officially confirm the victim's identity or release his body, saying they needed a DNA sample from next-of-kin.
The 45-year-old's wife and children, who were living in exile in the Chinese territory of Macau, have since gone into hiding over fears that his 21-year-old son, Kim Han-Sol, could be seen as a potential rival by his uncle Kim Jong-Un in a country roiled by bloody purges.
The brazen Cold War-style killing has triggered a bitter diplomatic row between the previously friendly Asian nations, which have expelled each other's ambassadors and refused to let their citizens leave.