Turkish police investigating the case had said in a statement on October 6 that 15 Saudis, including several officials, had arrived in Istanbul on two planes and entered the consulate while Khashoggi was inside.
Another unnamed government official told AFP that: "Based on their initial findings, the police believe that the journalist was killed by a team especially sent to Istanbul and who left the same day".
A group of 15 people from Saudi Arabia including some officials arrived in Istanbul in two planes and entered the consulate the same day Khashoggi was there and later left the country. He has not been heard of since.
According to a diplomatic source, Saudi Arabia's Ambassador to Ankara Waleed A.M. Elkhereiji was summoned to the Turkish Foreign Ministry on Sunday.
Erdogan's comments' came after media reports said his government sought permission from Saudi authorities to search the consulate premises in Istanbul.
Khashoggi has been missing since Tuesday when he had an appointment at the Saudi consulate to get papers needed to marry his Turkish fiancee. Turkey's Anadolu news agency also reported that the group of Saudis were briefly at the consulate.
Khashoggi spent a year ago in the USA in self-imposed exile, after he fled the kingdom amid a crackdown on intellectuals and activists who questioned the policies of Crown Prince Mohammed bin Salman. It has allowed reporters into the consulate to show Mr Khashoggi is not there. His abduction from Turkey-a North Atlantic Treaty Organisation ally (albeit a problematic one)-only furthers the brazenness of the Saudi plot against him.
The two regional heavyweights and U.S. allies have engaged in a delicate balancing of shared interests and opposing positions, sometimes teaming up to oppose President Bashar Assad in the Syrian conflict, for example, while sparring over Saudi Arabia's campaign to isolate Qatar and its regional fight against political Islam.
Khashoggi had gone to the consulate to receive an official document for their marriage.
Journalists and activists gathered outside the Saudi consulate on Monday demanding information on Khashoggi's fate. "The delegation is there to assist in the investigations regarding the disappearance of the Saudi citizen Jamal Khashoggi".
Khashoggi had been living in self-imposed exile in the United States since 2017, when he fled Saudi Arabia for fear of arrest.
"If this is true - that the Saudis lured a USA resident into their consulate and murdered him - it should represent a fundamental break in our relationship with Saudi Arabia", Murphy wrote on Twitter.
Mr Erdogan was more circumspect, saying on Sunday he remained "positive" and would await the results of an investigation as Turkish authorities continue to look at camera footage and airport arrivals and departures.
Ms Cengiz took to Twitter to say that she "did not believe he has been killed" and that she was waiting for official confirmation.
In an interview with Bloomberg, an American news service, he underscored that Riyadh "will pay nothing" to Washington for Saudi Arabia's security, adding that "all the armaments we have from the United States of America are paid for, it's not free armament". Saudi officials have denied the murder claims, insisting they are unaware of Khashoggi's whereabouts.
A spokesperson for the US State Department said it could not confirm the reports but was "closely following the situation".
While some stale conventional wisdom holds that the United States can not simultaneously stand for principles of human dignity while also maintaining stable relations with autocratic allies who share its other interests, there is ample precedent otherwise. She told the newspaper, "I can not think such an incident is acceptable to happen in Turkey".