He has told the media that Riyadh was being treated as “guilty until proven innocent”, adding that Saudi Crown Prince Mohammed Bin Salman has denied any knowledge of Khashoggi’s fate.
Trump tweeted that the crown prince had spoken to him on the phone and he “totally denied any knowledge of what took place in their Turkish Consulate”.
Trump said he “told me that he has already started, and will rapidly expand, a full and complete investigation into this matter. Answers will be forthcoming shortly”.
The Saudi heir apparent wields considerable power in the kingdom and is being held responsible by many outside for whatever happened to Khashoggi.
The phone call coincided with a visit to Saudi Arabia by US Secretary of State Mike Pompeo, sent to deal with the crisis in relations. Pompeo will head to Turkey on Wednesday, the BBC said.
Unnamed Turkish officials said a search of the Istanbul Saudi consulate has given more evidence that the Saudi critic was killed there, the BBC reported.
The Washington Post columnist, a strong critic of the Saudi leadership, was last seen alive entering the consulate on October 2.
Saudi Arabia has denied killing him and initially said he left the building “unharmed”. Earlier on Monday, The New York Times and CNN, quoting unnamed sources, reported that Saudi Arabia would acknowledge Khashoggi’s death was “the result of an interrogation that went wrong”.
The New York Times reported that four of the 15 people named by the Turkish authorities as suspects in Khashoggi’s disappearance have links to the crown prince, while another is a senior figure in the country’s Interior Ministry.
According to the newspaper, one of the men has been photographed accompanying the royal on his foreign visits. The case has put Saudi Arabia under pressure from close allies.
On Tuesday, G7 foreign ministers called for Saudi Arabia to conduct a “transparent” probe into the issue.
International Monetary Fund chief Christine Lagarde withdrew from a major Saudi investment meet adding to a long-list of high-profile absence from the event.
A search was to be conducted on Tuesday of the Saudi consul’s residence in Turkey, some 200 metres away from the consulate, where Khashoggi was last seen alive.
But it was delayed because no Saudi official was present for the joint investigation, the Turkish official added. The consul, Mohammad al-Otaibi, left Turkey on a commercial flight bound for Saudi Arabia earlier on Tuesday.
On the day of Khashoggi’s disappearance, several vehicles with Saudi diplomatic number plates were seen on video footage moving from the consulate to the residence.
Monday’s search of the consulate yielded evidence that Khashoggi was killed there, media reported. Samples, including soil from the garden and a metal gate, were reportedly taken.
Turkish authorities have already said they have audio evidence pointing to the murder.
Turkish President Recep Tayyip Erdogan told reporters the investigation “was looking into many things such as toxic materials and those materials being removed by painting them over”.