However, Saudi Arabia has offered no evidence to support its contention that the writer left the consulate unharmed and vanished into Istanbul while his fiancée waited impatiently outside.
US Secretary of State Mike Pompeo on Monday called for a thorough and open probe by Washington's ally Saudi Arabia into the disappearance of Riyadh critic Jamal Khashoggi, after US President Donald Trump voiced concern for the journalist.
The Saudi government, he said, was "fully cooperating" in the Turkish government's investigation.
Turkish officials have suggested Khashoggi was murdered.
Meanwhile on Tuesday, the Washington Post - where Khashoggi wrote columns after fleeing Saudi Arabia over fears of retribution for his critical commentary - reported United States intelligence intercepted communications of Saudi officials planning to abduct the prominent journalist. Saudi authorities have called the allegation "baseless".More news: How to be a better friend to someone with mental health issues
Bob Corker, who as chairman of the Senate Foreign Relations Committee has reviewed USA intelligence on the case, said it was likely that Khashoggi was killed the day he walked into the consulate. As a contributor to the Post, Mr Khashoggi has written extensively and critically about Saudi Arabia.
He has not been heard of since.
The United States is seeking more information, a State Department official said.
"Diplomats get absolute immunity from criminal prosecutions, so if an ambassador was involved in the murder, they can't be touched", Professor Saul said.
The Turkish Foreign Ministry has submitted a request to get the permission to inspect the Saudi consulate in Istanbul as part of the investigations of the disappearance of prominent Saudi journalist Jamal Khashoggi last week after entering the consulate.More news: Soyuz rocket carrying crew to ISS malfunctions during launch
"What was explained to us is this: He was killed, make your funeral preparations", Kislakci said.
TRT World's Ben Tornquist reports. "Because if he was alive, Saudis would provide evidence that he is alive", Yasin Aktay, an adviser to Turkish President Recep Tayyip Erdogan, tells CNN. And by mid afternoon on Sunday, no Turkish official had publicly accused Saudi Arabia of killing Khashoggi.
"We can not let this happen to reporters, to anybody", Mr Trump said on Wednesday.
Yemeni Nobel Prize victor Tawakkol Karman, centre, participates at a demonstration for Khashoggi that was organized by the Turkish-Arabic Media Association in front of the Saudi Arabian Consulate in Istanbul on Friday.
Erdogan, whose AK Party is rooted in political Islam, also supported a government in Egypt led by the Muslim Brotherhood, which Saudi Arabia has designated a terrorist movement. On Sunday, another official assessed it as "high probability" that Khashoggi was killed in the consulate and his body was taken away. Erdogan said of the consular officials at a news conference in the Hungarian capital, Budapest. If the Sauds conducted a hit on Khashoggi, they'll have to hope that no one talks and their allies eventually forget about it.
"His criticism, voiced over the past year, most surely rankles Mohammed bin Salman, who was elevated to crown prince last year and has carried out a wide-ranging campaign to silence dissent while trying to modernize the kingdom", the Post editorial read.More news: Google drops out of Pentagon's $10 billion cloud competition
BBC Newshour interviewed the journalist just three days before his visit to the consulate, and in an off-air conversation asked if he would ever return to his home country.
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