"It is absolutely essential to have a credible investigation and to have the punishment of those that were guilty," Guterres said at a conference in Doha.
The UN chief said he had no information on the case except what had been reported in the media.
Khashoggi, a Saudi contributor to the Washington Post, was killed on Oct. 2 shortly after entering the kingdom's consulate in what Riyadh called a "rogue" operation.
LR/PR