The Saudis continued to deny they killed the writer, but there were indications the story could soon change.
Khashoggi, a Washington Post contributor, vanished after entering the kingdom's Istanbul mission on October 2. "We're going to get to the bottom of it, and there will be severe punishment".
The statement did not directly acknowledge Khashoggi's disappearance, which happened October 2 when he visited the Saudi Consulate in Istanbul. The kingdom has called such allegations "baseless" but has not offered any evidence Mr Khashoggi ever left the consulate.
The dissident Saudi journalist's Turkish colleagues and several Turkish officials have voiced concerns that he was murdered in the consulate. The officials were not authorized to comment publicly on the matter and requested anonymity. Saudi state-owned company Aramco continued to supply a refinery in Canada despite Riyadh severing most other economic links.
The German, French and British foreign ministers said in a joint statement Sunday that defending freedom of expression and ensuring protection for journalists are key priorities and that they are "treating this incident with the utmost seriousness".
Trump quoted the King on Monday as saying that neither he nor his son, Crown Prince Mohammed, had any information about what had happened to Khashoggi.
The Saudi embassy in Washington later said Al Dakhil didn't represent the official position of the kingdom and Saudi officials, speaking privately, said there wasn't a change in the long-held policy that oil and politics don't mix. He and Trump's son-in-law and senior adviser, Jared Kushner, have forged close ties.
"Pointing out that US President Donald Trump had expressed anger after oil reached $80 a barrel, he asked readers to imagine what it would be like if it oil jumped to "$100, or $200, or even double that figure".
USA senators called for reactions ranging from boycotting an upcoming economic summit in Riyadh to ending support for Saudi military operations in Yemen.
On Sunday, Saudi Arabia's Ministry of Foreign Affairs emphasised the country's "leading position in the Arab and Islamic worlds" and claimed the country has "played a prominent role throughout history in achieving security, stability and prosperity of the region and the world, leading efforts in combating extremism and terrorism".
The New York Times, which was a media sponsor of the conference, has pulled out.
King Salman thanked Erdogan for welcoming a Saudi proposal to form a joint working group to discuss Khashoggi's disappearance and said that no one could undermine their relationship.
The Turkish inspection team included a prosecutor, a deputy prosecutor, anti-terror police and forensic experts, the state-run Anadolu news agency reported.
Cengiz said in the article that Khashoggi had been "cheerful" on the morning they traveled together to the consulate, and that the couple had made plans for the rest of their day.