Saudi Arabia's King Salman on Monday ordered an internal probe into the unexplained disappearance of prominent journalist Jamal Khashoggi as a joint Turkish-Saudi team was set to search the Saudi consulate in Istanbul where he was last seen on October 2.
U.S. President Donald Trump said meanwhile he had spoken with King Salman about Khashoggi, a critic of the kingdom's policies, and that he was sending Secretary of State Mike Pompeo to meet the king immediately.
Trump also said Salman denied "any knowledge of whatever may have happened" to Khashoggi, who disappeared after he went to the Saudi consulate in Istanbul two weeks ago, and told him the Saudis are working closely with Turkey on the case.
Khashoggi, a US resident and Washington Post columnist, vanished after entering the consulate to get marriage documents. Turkish officials have said authorities believe he was murdered and his body removed, allegations that Saudi Arabia has denied.
The case has provoked an international outcry, with Trump threatening "severe punishment" if it turns out Khashoggi was killed in the consulate and European allies urging "a credible investigation" and accountability for those responsible.
A Turkish diplomatic source said investigators would inspect the consulate on Monday afternoon, after delays last week when Turkey accepted a Saudi proposal to work together to find out what happened to Khashoggi.
"The King has ordered the Public Prosecutor to open an internal investigation into the Khashoggi matter based on the info from the joint team in Istanbul," a Saudi official, not authorised to speak publicly, told Reuters.
Asked when the public prosecutor could make an announcement about the investigation, the official said: "He was instructed to work quickly."
Britain expects Riyadh to provide "a complete and detailed response" to questions over Khashoggi's disappearance, Prime Minister Theresa May's spokesman said on Monday.
Saudi Arabia has responded to Western statements by saying it would retaliate against any pressure or economic sanctions "with greater action", and Arab allies rallied to support it, setting up a potential showdown between the world's top oil exporter and its main Western allies.
King Salman and Turkish President Tayyip Erdogan spoke by telephone on Sunday evening and stressed the importance of the two countries creating a joint group as part of the probe.
Broadcaster CNN Turk reported on Monday that the Saudi team had arrived at Istanbul police headquarters.
The Saudi riyal fell to its lowest in two years and its international bond prices slipped over fears that foreign investment inflows could shrink amid international pressure.
The Saudi stock market had tumbled 7.2 percent over the previous two trading days but rebounded 2 percent on Monday.
Foreign capital is key to Saudi plans for economic diversification and job creation.
But concern over the disappearance has seen media organisations and a growing number of attendees pull out of a "Davos in the Desert" investment conference set for Oct. 23-25, which has become the biggest show for investors to promote Saudi Crown Prince Mohammed bin Salman's reform vision.
On Monday, a source familiar with the matter said Blackstone CEO Stephen Schwarzman and BlackRock Chief Executive Larry Fink were pulling out of the summit. Both companies declined comment.
Saudi Arabia's Public Investment Fund (PIF), which hosts the conference, has tentatively committed $20 billion to an infrastructure investment planned with Blackstone Group. Prince Mohammed told Reuters last year that Blackstone and BlackRock Inc were planning to open offices in the kingdom.
Bahrain called for a boycott of Uber, in which PIF has invested $3.5 billion, after its chief executive officer said he would not attend the conference.
Similar campaigns trended on social media in Saudi Arabia and the United Arab Emirates. UAE businessman Khalaf Ahmad Al-Habtoor urged a boycott of Virgin, which has suspended discussions with PIF over a planned $1 billion investment.
Khashoggi, a familiar face on Arab talk shows, moved to the United States last year fearing retribution for his criticism of Prince Mohammed, who has cracked down on dissent with arrests.
The former newspaper editor once interviewed Osama bin Laden and later became a consummate insider, advising former Saudi intelligence chief Prince Turki al-Faisal when he served as ambassador in London and Washington.
A pro-government Turkish daily published preliminary evidence last week from investigators it said identified a 15-member Saudi intelligence team which arrived in Istanbul on diplomatic passports hours before Khashoggi disappeared.
The Saudi consulate referred Reuters to authorities in Riyadh who did not respond to questions about the 15 Saudis.