WASHINGTON (BLOOMBERG) - President Donald Trump added to the pressure on Saudi Arabia over the fate of Washington Post writer Jamal Khashoggi, vowing "severe punishment" should the kingdom's leaders be linked to his disappearance.

But at a White House event with US pastor Andrew Brunson, who arrived in Washington after being freed in Turkey, Trump said the US would be "foolish" to cancel arms deals with the Kingdom in response to the controversy.

If the US moves aside, China and Russia would be ready to swoop in and get the business, Trump said.

"Nobody knows" whether Saudi officials are involved although they "deny it vehemently," Trump said in an excerpt of a CBS News 60 Minutes interview to be broadcast Sunday night.

"It's being looked at very, very strongly. We would be very upset and angry if that was the case."

"We're going to get to the bottom of it, and there will be severe punishment," the president said. "Could it be them? Yes."

Khashoggi, a Saudi critic of the regime, hasn't been seen since he entered the Saudi consulate in Istanbul on Oct 2 to pick up a document for his upcoming wedding.

Turkish officials say they have audio and video recordings that show a Saudi security team detained Khashoggi in the consulate before killing him and dismembering his body, the Post reported. Saudi officials say Khashoggi left the building unharmed.

The affair is eclipsing the three-day Future Investment Initiative, known as "Davos in the Desert," that is scheduled to start in Riyadh in just two weeks. The event is intended to showcase Prince Mohammed bin Salman's modernisation plan for the desert kingdom.

"What has reportedly happened in Turkey around the disappearance of journalist Jamal Khashoggi, if proved true, would clearly change the ability of any of us in the West to do business with the Saudi government," said billionaire Richard Branson, who suspended talks with the Saudi Public Investment Fund over a possible stake in his space companies Virgin Galactic and Virgin Orbit. He said he also was suspending his directorships in Saudi Red Sea tourism projects.

Other company leaders who've said they will not attend the summit because of the Khashoggi case include Viacom chief executive officer Bob Bakish; Los Angeles Times owner Patrick Soon-Shiong; HP executive Joanna Popper; Andy Rubin, creator of the Android mobile operating system; and Rodger Novak, co-founder of Crispr Therapeutics.

Uber Technologies CEO Dara Khosrowshahi won't attend "unless a substantially different set of facts emerges."

Several companies including Bloomberg have pulled out of the event as media partners.

US lawmakers have threatened to take action against the kingdom such as blocking arms sales.

In the 60 Minutes interview, Trump said new actions should not jeopardize the Saudi military equipment contracts held by companies such as Boeing, Lockheed Martin and Raytheon, which he said would put jobs at risk.

'HARSH WORD'

"I don't want to hurt jobs. I don't want to lose an order like that," he said. "There are other ways of punishing, to use a word that's a pretty harsh word, but it's true."

Trump's hesitation to strike back at the kingdom reflects close ties the White House has nurtured with the nation's de facto ruler, the crown prince, and his administration's acquiescence to other Saudi actions that have drawn international condemnation.

Under Trump, the US has continued to back a Saudi bombing campaign against Houthi rebels in neighbouring Yemen that has killed thousands of civilians, providing American logistical support and weapons.

Part of Prince Mohammed's plan to overhaul the Saudi economy is an attempt to attract foreign direct investment into the kingdom. In an interview with Bloomberg last week, he said the three-day event would see the sealing of a major investing agreement in the non-oil economy.

US Treasury Secretary Steven Mnuchin and International Monetary Fund Director Christine Lagarde told reporters in Bali, Indonesia, on Saturday they still plan to attend.

"Horrifying things have been reported, and I am horrified. But I have to conduct the business of the IMF in all corners of the world," Lagarde said in Bali, where the annual IMF meetings are taking place.

It's not the first time controversy has overshadowed the FII event. Scores of the kingdom's businessmen, princes and officials were rounded up in the Ritz-Carlton hotel just days after last year's conference in what the government described as a crackdown on corruption.

Last year, Prince Mohammed used the FII to unveil plans for Neom, a US$500 billion high-tech mega city. The venture attracted former US energy secretary Ernest Moniz to its advisory board. Sam Altman, president of tech incubator Y Combinator, suspended his involvement with the Neom board. Moniz took the same action until more is known about Khashoggi's fate, Axios reported.