The Saudi source said that a security team including Saudi investigators had arrived in Istanbul on Saturday to take part in the investigation into Khashoggi's disappearance.
Saudi Arabia has denied the accusations, saying it is "working to search for him".
When was he last seen?
However, Erdogan - who said he was personally following the case - said Turkey had no documents or evidence at hand regarding the case.
"If Khashoggi's death is confirmed and accusations against the Saudis hold, the image of the "reformer" crown prince becomes more hard to swallow particularly in Washington and other Western capitals", she told AFP.
However, Khashoggi's other friend, the well-known Brotherhood leader Azzam al-Tamimi, expressed his disappointment regarding the Turkish denial and strongly criticized Erdogan for that.
"Jamal is not dead!" Ms Cengiz wrote in a Twitter post that included a photo of Mr Khashoggi.
"We are ready to welcome the Turkish government to go and search our premises", he said.
Turkey has been coy and giving conflicting statements about what they believed to have happened to Mr. Khashoggi and certainly Turkey's own bleak record of mistreatment and jailing of its journalists is being used by Saudi authorities to pour added doubt on the case.
20 killed in upstate NY crash involving limo
Axel Steenburg , left, and his brother Rich Steenburg, right, were both killed, according to their stepfather, Lester Andrews. The crash occurred just before 2pm on Saturday afternoon (local time) in Schoharie, about 60km west of Albany, on Route 30.
When Kristian Ulrichsen, a Rice University professor, responded to Nuseibeh's tweet with a question about Khashoggi's location, Nuseibeh had a curt response that again deflected attention from the Saudis: "Ask Erdogan and Tamim", referring to Turkish President Recep Tayyip Erdogan and Qatar's ruler Tamim bin Hamad Al Thani.
What have the Saudis said?
He said if allegations of the Saudi journalist's murder are true, it is a violation of the Vienna Convention on Diplomatic Relations and those who violate it should leave Turkey. It has allowed reporters into the consulate to show Mr Khashoggi is not there.
The Saudi Crown Prince refuted the claims later in an interview during which he said Turkey can search the kingdom's consulate in Istanbul for the Saudi journalist, saying: "We have nothing to hide". He writes out of a sense of love for his country and deep faith in human dignity and freedom, ' Hiatt said in a statement on the U.S. newspaper's website. But if proven, the murder of Jamal Khashoggi would be the most serious diplomatic crisis between the two in living memory.
Saudi Arabia has long run a murderous regime that also uses "anti-terror" legislation to jail human rights defenders.
He is a high-profile critic of the crown prince. Saudis are not permitted to champion or intellectually argue for reform, they are only takers of change granted from the megalomaniac, brash Crown Prince.
He 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.
One week after Khashoggi's disappearance at the Saudi facility in Istanbul, the official Saudi line remains that the kingdom is as confused as everyone else.
"I have left my home, my family and my job, and I am raising my voice", he wrote in September.
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.
"It anguishes me to speak with other Saudi friends in Istanbul and London who are also in self-exile".