US officials have also said that the crown prince of Saudi Arabia, Mohammed bin Salman, ordered an operation to lure Khashoggi from his home in Virginia back to Saudi Arabia and then to detain him, according to USA intelligence intercepts of Saudi officials discussing the plot.
Already, worldwide business leaders are pulling out of the kingdom's upcoming investment forum, a high-profile event known as 'Davos in the Desert'. The kingdom's Tadawul All-Shares Index later clawed back some losses to close down 3.5 percent.
Concerns appeared to spread Monday to Japan's SoftBank, which has invested tens of billions of dollars of Saudi government funds.
U.S. President Donald Trump has threatened "severe punishment" if it turns out Khashoggi was killed in the consulate, although he said Washington would be "punishing" itself if it halted military sales to Riyadh.
Asked when the public prosecutor could make an announcement about the investigation, the official said: "He was instructed to work quickly".
In an interview to be aired Sunday, Trump told CBS' "60 Minutes" that "We're going to get to the bottom of it and there will be severe punishment".
A statement issued by the Kuwaiti Cabinet on Monday said Kuwait rejects all the accusations and unlawful campaigns targeting Saudi Arabia.
But if the Saudis retaliate using oil, it would lead to "calamity", said Stephen Innes, Singapore-based head of Asia Pacific trading at Oanda Corp.
Trump's statement came as CNN cited two sources as saying the Saudis were preparing to report that Khashoggi died as the result of a botched interrogation, while the Wall Street Journal said the kingdom was weighing whether to say that rogue operatives killed Khashoggi by mistake.
The Saudi foreign ministry said Mr Salman affirmed his country's "solid" relations with Turkey in the phone call with Mr Erdogan.More news: Is there a Huawei Mate 20 with a stylus coming?
The statement did not elaborate. A Saudi-owned satellite channel later suggested the world's largest oil exporter could wield that production as a weapon against America.
Trump also seemed to offer another theory for a crime allegedly carried out at the Saudi diplomatic post.
"If President Trump was angered by $80 oil, nobody should rule out the price jumping to $100 and $200 a barrel or maybe double that figure", he wrote.
The Saudi Gazette trumpeted: "Enough Is Enough", while the Arab News said: "Saudi Arabia "will not be bullied".
Rubio declined to rule out a halt to the arms sales, stressing that the US must send a message to repressive governments worldwide. Later that same day, however, the Saudi embassy in Washington tweeted a clarification that pretty much dismissed the tone of the official source's warning reported by the SPA.
Earlier on Monday, Salman ordered an internal probe into Khashoggi's disappearance while a joint Turkish-Saudi team was set to search the consulate.
While Turkey and the kingdom differ on political issues, Saudi investments are a crucial lifeline for Ankara amid trouble with its national currency, the Turkish lira.
Prince Mohammed told Reuters past year that Blackstone and BlackRock Inc were planning to open offices in the kingdom.
SoftBank is now one of the world's most prolific investors, through its "Vision Fund"-a $100 billion war chest that was established a couple years back with a $45 billion infusion from Saudi Arabia's sovereign wealth fund. Recipients of Vision Fund investments have included ride-hailing outfits such as Uber and Didi Chuxing, GM's Cruise self-driving vehicle subsidiary, chipmakers ARM and Nvidia, and the office-space firm WeWork".