But President Trump, who also has Saudi business ties, says he does not want the U.S.to cancel lucrative military contracts with the kingdom.
In a joint statement on Sunday, France, Germany, and the United Kingdom said that "light must be shed" on the disappearance of the US-based journalist Jamal Khashoggi, who had not been seen since entering the Saudi consulate in Istanbul earlier this month.
White House economic adviser Larry Kudlow declined to speculate on what Trump might do, citing a "swift and transparent investigation" in the coming week.
Saudi King Salman called President Recep Tayyip Erdoğan, thanking him for the recently formed joint Turkish-Saudi working group to investigate the disappearance of journalist Jamal Khashoggi, who is feared to have been murdered by a team of Saudi agents in the kingdom's Istanbul consulate.
Saudi officials call all the allegations "baseless", but have offered no evidence Mr Khashoggi left the consulate.
Reports suggest an assault and struggle took place in the consulate after Mr Khashoggi entered the building to get some documents.
The latest cancellations could add pressure on other United States firms like Goldman Sachs Group Inc, Mastercard Inc and Bank of America Corp to reconsider their plans to attend the event.
Saudi Arabia's Tadawul All-Shares Index (TASI) lost more than 500 points on the first trading day of the week on Sunday, wiping out all the gains it had made since the start of the year.
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It was just a situation where it was sore. "It's hard for me to reflect too much right now just because my career's not done". Peterson said he dislocated the joint during the first half of a 43-19 loss to the New Orleans Saints on Monday.
"One possible area of cooperation for the Turkish and Saudi authorities is how to make Khashoggi's disappearance disappear from the public limelight".
Jamal Khashoggi, a well-known journalist and critic of the Saudi government, has not been seen since he attended Saudi Arabia's consulate in Istanbul last week.
There's now some doubt about whether US Treasury Secretary Steven Mnuchin will attend the Riyadh conference. But Trump has said he does not want to halt a proposed $110 billion arms sale to Saudi Arabia because, he maintained, it would harm USA manufacturers.
US lawmakers, for their part, have come out more strongly.
The Crown Prince has launched a series of social reforms in Saudi Arabia, including allowing women to drive. Western banks have also hoped to help the kingdom privatize its giant oil company, Saudi Aramco, although the country's plans for an initial public offering appear to have stalled.
Business barons including British billionaire Richard Branson and Uber CEO Dara Khosrowshahi, as well as media powerhouses like Bloomberg and CNN, have all pulled out.
"Well, nobody knows yet, but we'll probably be able to find out", Trump said in the interview with Lesley Stahl of CBS's 60 Minutes, which will air in full today.
The nature of the act - a brazen alleged murder at a diplomatic mission in Istanbul - may give Turkey a further incentive to hope the Khashoggi issue will just go away, according to Teneo's Piccoli.
Rubio's comments come a day after Trump vowed "severe punishment" for the U.S. ally if they were found responsible.