In a statement issued after two days of talks with Saudi Arabia's public prosecutor Saud al-Mojeb, it also said no concrete results were reached in those meetings.
Khashoggi's death has escalated into a crisis for Saudi Arabia, the world's top oil exporter, which at first denied any knowledge of or role in his disappearance on Oct. 2.
Mojeb later said Khashoggi's killing was premeditated and Riyadh said 18 suspects had been arrested. But Turkey, which released a stream of evidence undermining Riyadh's early denials, has demanded more details including the whereabouts of Khashoggi's body and who ordered his killing.
"Despite our well-intentioned efforts to reveal the truth, no concrete results have come out of those meetings," the Istanbul prosecutor's office said of the talks on Monday and Tuesday between Mojeb and Istanbul chief prosecutor Irfan Fidan.
The killing of Khashoggi, a critic of de facto ruler Crown Prince Mohammed bin Salman, has put into focus the West's close relationship with Saudi Arabia - a major arms buyer and lynchpin of Washington's regional plans to contain Iran.
President Tayyip Erdogan, who has demanded more information from Saudi Arabia, said on Tuesday Fidan had asked Mojeb to disclose who sent a 15-strong team from Riyadh which is suspected of involvement in the killing. (Reporting by Ece Toksabay and Ali Kucukgocmen Editing by Dominic Evans and Angus MacSwan)
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