The Foreign Ministers of the United Kingdom, France and Germany on Sunday expressed serious concerns about the fate of a missing Saudi Arabian journalist and called for an investigation into the case.
Khashoggi, a US resident and Washington Post columnist critical of Riyadh's policies, disappeared on October 2 after entering the Saudi consulate in Istanbul.
They said there must be a credible investigation to establish the truth and "if relevant" identify those responsible for Khashoggi's disappearance.
Saudi Arabia is also reversing their cooling rhetoric on oil prices, warning that the Saudi government will not be hitting its oil production quotas, and will no longer rule out barrels hitting $100 or even higher, in a direct threat to President Trump's current stance on oil prices, who has frequently demanded that OPEC nations including Saudi Arabia do more to suppress currently-rising oil costs across the globe. "We have conveyed this message directly to the Saudi authorities", the statement added.
Turkish officials say they have audio and video recordings that show a Saudi security team detained Mr Khashoggi in the consulate before killing him and dismembering his body, the Post has reported.
Earlier this year, Switzerland and Saudi Arabia boosted cooperation on financial matters.
Flake said if the Saudis did, in fact, kill Khashoggi, Congress might specifically curtail US military aid to Saudi-led forces in Yemen.
"There's something really bad and disgusting about that, if that was the case, so we're going to have to see", Trump said. "I've heard that report but nobody's knows if it's an official report".
Prince Mohammed, King Salman's son, has aggressively pitched the kingdom as a destination for foreign investment.
Sunday's plunge in the Saudi bourse was the worst in years and came after US President Donald Trump threatened Riyadh with "severe punishment" if Khashoggi was killed inside its Istanbul mission. He and Trump's son-in-law and senior adviser, Jared Kushner, have forged close ties.
Saudi Arabia has pledged to retaliate economically for any US punitive action.
The Swiss government could decide on a case-by-case basis whether to impose economic sanctions on Saudi Arabia, a SECO spokesman said.
There's now some doubt about whether US Treasury Secretary Steven Mnuchin will attend the Riyadh conference. "Because of the leadership, because of the location, because of the people in the kingdom, we can make it happen".
"It's being investigated, it's being looked at very, very strongly", Trump said. Several business leaders and media outlets have backed out of the upcoming investment conference in Riyadh, called the Future Investment Initiative.
And Rubio said that no US government officials should be attending the Saudi conference until they get some official answers about what happened. They include the CEO of Uber, a company in which Saudi Arabia has invested billions of dollars; billionaire Richard Branson; JPMorgan Chase & Co.