Istanbul, Turkey (CNN) The body of Saudi journalist Jamal Khashoggi was dismembered after he was strangled as soon as he entered the Saudi consulate in Istanbul, the chief prosecutor's office in Istanbul said Wednesday.

This was carried out as part of a premeditated plan, according to a statement by the chief prosecutor's office.

The statement is the clearest yet from the Turkish authorities about the fate of the Washington Post journalist, whose remains have not yet been found.

"The victim's body was dismembered and destroyed following his death by suffocation," the statement said.

"In accordance with plans made in advance, the victim Jamal Khashoggi, was choked to death immediately after entering the Consulate General of Saudi Arabia in Istanbul on October 2, 2018."

Turkish President Recep Tayyip Erdogan on Friday demanded that Saudi Arabia reveal the location of Khashoggi's body and hand over 18 suspects

The Saudis have presented shifting stories about Khashoggi's fate, initially denying any knowledge before arguing that a group of rogue operators, many of whom belong to Saudi Crown Prince Mohammed bin Salman's inner circle, were responsible for Khashoggi's death. The Saudi attorney general then acknowledged that Khashoggi was killed in a premeditated murder

Turkish investigators continue to look for clues to the whereabouts of his body.

Security camera footage shows Jamal Khashoggi entering the Saudi consulate on October 2.

A source close to the Saudi Royal Palace told CNN last week that the location of Khashoggi's body was not known to the Saudis. The source said the body was handed over to a local "collaborator" after the killing, adding that it is not at the Saudi consulate in Istanbul.

"We have requested information from Saudi officials regarding the whereabouts of Jamal Khashoggi's body and the identity of the supposed local collaborator. We also noted that Saudi Arabia must extradite all 18 suspects to Turkey so that they can be held accountable for what they did," a senior Turkish official told CNN on Wednesday.

"The Saudi officials seemed primarily interested in finding out what evidence the Turkish authorities had against the perpetrators. In other words, we did not get the impression that they were keen on genuinely cooperating with the investigation," the official said.

The Saudi chief prosecutor arrived in Turkey on Sunday to meet with his Turkish counterpart. Turkish state news agency Anadolu reported that he had boarded a plane back to Saudi Arabia on Wednesday, having met with the Istanbul chief prosecutor twice.

The chief prosecutor's office in Istanbul said that during those meetings, Turkey and Saudi Arabia had "agreed to investigate, search and uncover all details of the event from all angles and to bring those who carried out and planned it to ... justice."

But, the statement said, the Saudis had not answered three questions the Turkish side posed -- namely, where Khashoggi's body is; whether Saudi investigators had uncovered evidence about the planning of his killing; and the identity of the reported "local collaborator."

Instead, it said, the Saudis on Wednesday invited the Turkish prosecutor and his delegation to Saudi Arabia jointly to question the suspects held there about what happened to Khashoggi's body and whether his death was premeditated. The Turks added that the Saudi prosecutor also said no statement had been made by Saudi authorities about the existence of the purported local cooperator.

"Despite our well-intentioned efforts to reveal the truth, no concrete results have come out of those meetings," the Istanbul chief prosecutor's office said, adding that it was in this light that it had been "obliged" to share the details about how Khashoggi was strangled and his body "dismembered and destroyed," in accordance with plans made in advance.

The Saudi government has said it will carry out a thorough and transparent investigation and that the suspects will be prosecuted in Saudi Arabia.

After Saudi Arabia admitted that Khashoggi was killed in its Istanbul consulate, five high-ranking officials were dismissed, including bin Salman's media chief and the deputy head of the Saudi intelligence service. Eighteen people were arrested.

Riyadh has maintained that neither bin Salman nor King Salman knew of the operation to target Khashoggi. US officials have said such a mission -- including 15 men sent from Riyadh -- could not have been carried out without the authorization of bin Salman, the country's de facto ruler.