Earlier on Saturday Turkish officials said prosecutors had begun investigating Khashoggi's disappearance and a spokesman for President Tayyip Erdogan's AK Party said authorities would uncover his whereabouts.
Turan Kislakci, a friend of Jamal Khashoggi and the head of the Turkish-Arab Media Association, told The Associated Press on Sunday that officials also told him they "have evidence he was killed in a barbaric way" and dismembered.
"If Khashoggi was indeed murdered inside a diplomatic facility, it is an act of terror that echoes Russian and Chinese tactics of extraterritorial, extrajudicial attacks on dissidents, meant to intimidate any who would speak out against the Saudi government, no matter where they may be, and giving the lie to official narratives of "reform" in Saudi Arabia", said Summer Lopez, of PEN America.
He said the consulate was equipped with cameras but they did not record footage, so no images could be retrieved of Khashoggi entering or leaving the consulate, which is ringed by police barriers and has high security fences topped with barbed wire.
Khashoggi had lived in self-imposed exile in Washington for the past year, saying he feared retribution for his criticism of Saudi policies including the war in Yemen and a crackdown on dissent in which dozens of people have been detained.
In an interview with Bloomberg last week, Crown Prince Mohammed bin Salman said Khashoggi had left the consulate shortly after he arrived on Tuesday.
Khashoggi's fiancee could not immediately be contacted but she said in a Tweet that there had been no official confirmation of the Turkish sources' statements.
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"We are ready to welcome the Turkish government to go and search our premises", he said, which is Saudi sovereign territory. On Wednesday, the Turkish foreign ministry summoned the Saudi ambassador and asked for an explanation about the disappearance.
"We are not in a position to confirm these reports, but we are following them closely", the official said. And we will continue our dialogue with the Turkish government to see what happened to Jamal there.
The journalist said he had been banned from writing in the pan-Arab daily Al-Hayat, owned by Saudi prince Khaled bin Sultan al-Saud, over his defence of the Muslim Brotherhood which Riyadh has blacklisted as a terrorist organisation.
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. For years he was seen as being close to the Saudi royal family.
Khashoggi may have been considered especially unsafe by the Saudi leadership, analysts said.
As they pushed to liberalize the ultraconservative country, King Salman and his powerful son, Crown Prince Mohammed bin Salman, have overseen a sweeping crackdown on dissidents.
Khashoggi was born in the western Saudi city of Medina, revered in Islam as the burial place of the Prophet Mohammed.