USA intelligence officials reportedly intercepted communications that the Saudis discussed a plan to lure and capture Khashoggi before his disappearance.
"I also urge Saudi Arabia, especially King Salman and Crown Prince Mohammed bin Salman, to show the same level of sensitivity and release CCTV footage from the consulate", wrote Hatice Cengiz, who lives in Istanbul.
Saudi Arabia asserts the allegations are "baseless".
Khashoggi, a former Saudi government adviser, had been living in the United States since a year ago fearing possible arrest.
The Saudi consulate referred Reuters to authorities in Riyadh who have not responded to questions about the 15 Saudis, who arrived in the city hours before he went missing on October 2.
Khashoggi, 59, who was once close to the Saudi royal family and has served as an adviser for senior Saudi officials, left the country past year to live in the United States in self-imposed exile, saying he feared retribution for his criticism of Saudi policy in the Yemen war and its crackdown on dissent.
But Turkish officials have concluded that whatever the intent of the operation, Khashoggi was killed inside the consulate. The footage does not show Khashoggi himself leaving the consulate. This is the way the most brutal, heinous regimes in the world behave....
Riyadh and Ankara have also differed on the subject of the Muslim Brotherhood in Egypt and on the Israeli-Palestinian conflict, where Saudi Arabia has unofficially backed the so-called U.S. "deal of the century", whereas Turkey has condemned the Trump administration's attempt to "force a deal on the Palestinians". Bob Corker (R-Tenn.) told reporters Wednesday that the Senate would "take some action" regarding the journalist's disappearance.
The disappearance of journalist Jamal Khashoggi on Wednesday prompted senators to initiate an investigation and possible sanctions against Saudi Arabia. "I very much doubt we could pass another one", Corker said.
Under pressure from Congress, the Trump administration faces a dilemma: how to respond to the disappearance of Saudi journalist Jamal Khashoggi while ensuring that any punitive action does not alienate Riyadh, a key ally against Iran.
President Donald Trump says the U.S.is "demanding" answers from Saudi Arabia about missing Saudi journalist Jamal Khashoggi and wants to bring his fiancee to the White House. His move to the United States was prompted by concerns he'd be detained in Saudi Arabia or banned from travel as he became increasingly alienated from the leadership. "They played him like a dolt".
"We knew of Jamal's interest in building platforms to promote the discussion of issues that he is passionate about, notably freedom and democracy in the Middle East", he told the Daily Beast.
Trump, speaking to reporters in the Oval Office, said he's spoken "more than once" with the Saudis in recent days but didn't provide details of the conversation.