A statement from the office of prosecutor Irfan Fidan said meetings with his Saudi Arabian counterpart, who visited Istanbul this week, had produced "no concrete results" on the killing, which it said was premeditated.
Khashoggi, a 59-year-old columnist for The Washington Post, vanished after entering the consulate in Istanbul on October 2 to pick up paperwork for his upcoming marriage to his fiancee, who was waiting for him outside. A critic of the Saudi royal family, Khashoggi had been living in exile in the United States.
The statement comes hours after Saudi Arabia's chief public prosecutor ended his visit to Istanbul, during which he met Fidan twice and visited the kingdom's consulate and the regional offices of the Turkish intelligence agency.
Saudi Attorney General Sheikh Saud al-Mojeb reportedly refused to share information from Riyadh's own investigation.
"In accordance with plans made in advance, the victim, Jamal Khashoggi, was strangled to death immediately after entering the consulate on October 2," the Istanbul prosecutor's office said in a statement.
"The victim's body was dismembered and destroyed following his death by suffocation -– again, in line with advance plans," it added.
Turkish authorities said they were not satisfied after the talks with the Saudi prosecutor.
"Despite our well-intentioned efforts to reveal the truth, no concrete results have come out of those meetings," the Istanbul prosecutor's office said.
And contrary to media reports, Mojeb also said no statement was made by the Saudi authorities that the body was given to a "local cooperator," according to the Istanbul prosecutor's office.
Turkey is seeking the extradition of 18 Saudi suspects detained in Saudi Arabia over the killing of Khashoggi. It is also pressing Saudi Arabia for information concerning Khashoggi's remains, which still haven't been found, as well as who ordered the journalist's slaying. Turkish President Recep Tayyip Erdogan has also called on Riyadh to disclose the identity of an alleged local collaborator said to have been involved in disposing of Khashoggi's body and who ordered the hit.
Turkey alleges a Saudi hit squad from Saudi Arabia — including a member of Saudi Crown Prince Mohammed bin Salman's entourage during a trip to the United States— traveled to Istanbul to kill the journalist and then tried to cover it up.
Under mounting pressure, Saudi Arabia changed its narrative about Khashoggi's killing several times, eventually admitting that Khashoggi died inside the consulate and only recently acknowledging that Turkish evidence shows his killing was premeditated.
Saudi Arabia has not commented on the prosecutor's visit.
AFP and AP contributed to this story.