The Post reported Saturday that Turkey had concluded Khashoggi, a recent critic of the desert kingdom's leadership, was killed by a Saudi team specifically sent to Istanbul for the murder, according to two people with knowledge of the investigation.
Reacting to the news of the alleged murder, the journalist's Turkish fiancee, Hatice Cengiz, said on Twitter she "did not believe he has been killed".
The police said that around 15 Saudis, including officials, came to Istanbul on two flights on Tuesday and were at the consulate at the same time as the journalist.
Fears are growing over missing Washington Post writer Jamal Khashoggi, after Turkish officials said they believe he has been murdered. Another official confirmed the story. "We called a few other places, these are lower officials, but they said: 'We have evidence he was killed in a barbaric way, we will announce it tomorrow or the day after"'.
Fearing he would be arrested or banned from traveling outside the kingdom, Mr. Khashoggi left his home country a year ago and moved to Washington, D.C., where he lived in self-imposed exile.
He also said what happened to Khashoggi was a crime and those responsible for his disappearance must be tried, Al Jazeera said.
Khashoggi has also criticised Saudi Arabia's role in Yemen, where Riyadh leads a military coalition fighting alongside the government in its war with Iran-backed rebels.
"The 33-year-old crown prince went on to say that Saudi Arabia had agreed to buy $110 billion worth of U.S. weapons and signed investment deals worth billions more, some $400 billion in total, since Trump took office in early 2017, and described the deals as a good achievement" for Trump.
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Earlier, Prince bin Salman told Bloomberg News that Turkish authorities were welcome to search the building.
"Advocates of liberty and freedom of thought in Turkey will follow this case closely", said Erdoğan and added, "I, as President of Turkey, personally follow this case closely as well". But he added that diplomatic cars had been seen moving in and out.
The source further said that the interrogators later dismembered his body and the Saudi nationals took interrogation video with themselves to brief Saudi Crown Prince Mohammed bin Salman on his death, the source said.
The Committee to Protect Journalists said it was alarmed by reports Khashoggi may have been killed inside the consulate.
"Everyone heard about the rumours of Saudi Arabia cancelling the IPO of Aramco, delaying that, and that this is delaying Vision 2030", he said. "We have nothing to hide".
Once regarded as close to the Saudi establishment, he was a frequent defender of the kingdom's policies.
Never one to mince his words, Khashoggi described a new Saudi era of "fear, intimidation, arrests and public shaming" in an article published in the Post a year ago.
He went to the Saudi consulate to obtain an official document for his upcoming marriage to his Turkish partner.