Among those who dropped out are International Monetary Fund chief Christine Lagarde, JPMorgan Chase CEO Jamie Dimon, Blackstone CEO Stephen Schwarzman, as well as the chiefs of Uber, BlackRock, MasterCard and Viacom.
A number of media outlets including CNBC, The New York Times, Bloomberg, CNN and the Financial Times have also withdrawn from the event, which is scheduled for Tuesday through Thursday in the Saudi capital Riyadh.
Khashoggi, a Saudi Arabian journalist who contributed to The Washington Post and lived in the United States, has not been seen since entering the Saudi consulate in Istanbul on Oct. 2. Turkish authorities have accused the Saudi government of dismembering and killing Khashoggi.
Reports in Turkish state news outlets and The New York Times, have said suspects in the disappearance have close ties to Saudi Crown Prince Mohammed bin Salman. The Saudi government has denied any involvement in the alleged killing.
Crown Prince Mohammed has sought to bring his country closer to the United States as a trade partner and has developed close ties with President Donald Trump's son-in-law and senior advisor, Jared Kushner.
Trump has expressed doubt that Khashoggi was murdered by the Saudis and has floated, without evidence, the possibility that the dissident was targeted by "rogue killers." In a statement posted to Twitter minutes after Mnuchin's announcement, the president wrote that his administration was awaiting the results of Turkish and Saudi Arabian investigations into the matter.
Earlier Thursday, Secretary of State Mike Pompeo, whom Trump dispatched to Saudi Arabia and Turkey to meet with officials there, told reporters that Saudi Arabian officials "assured me that they will conduct a complete and thorough investigation."