Erdogan also said Saudi's public prosecutor was due to meet the Istanbul prosecutor in Istanbul on Sunday.
Saudi Arabia will prosecute the suspects in the murder of prominent journalist Jamal Khashoggi, the kingdom's Foreign Minister Adel bin Ahmed Al-Jubeir said Saturday after Turkey called for their extradition.
At a conference in Riyadh on Wednesday, the crown prince said the killing was a "heinous crime that can not be justified" and warned against any efforts to "manipulate" the crisis and drive a wedge between Saudi Arabia and Turkey, which are regional rivals but also diplomatic and business partners. After weeks of denying knowledge of whereabouts, and changing its story a number of times, Riyadh has said his killing was premeditated.
Media captionJamal Khashoggi: What we know about the journalist's disappearance and death What else did his fiancée say?
The killing took place inside the Saudi consulate in Istanbul Oct. 2-and at the hands of US ally and major arms buyer Saudi Arabia.
However, world leaders including Prime Minister Theresa May and President Trump have called the Saudi's account "not credible" with the U.S. leader saying it was the "worst cover up in the history of cover ups".
For decades, Mr Khashoggi was close to the Saudi royal family.
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"My demand is that 18 people be tried in Istanbul", Erdogan said in an address to lawmakers from his ruling party at parliament in Ankara on Tuesday.
Saudi authorities earlier arrested 18 men wanted by Ankara following an global furore over the death of Khashoggi, a Washington Post contributor and critic of Saudi policies, who was killed at the Saudi consulate in Istanbul on October 2.
In a tearful television interview on Friday, Ms Cengiz recounted the day her fiancé vanished, saying she would never have let her partner enter the consulate if she had thought that the "Saudi Arabia authorities would hatch a plot" to kill him.
"The issue, as I said, is being investigated".
In the aftermath of Khashoggi's killing inside the Saudi Consulate on October 2, Saudi Arabia has offered shifting explanations for what happened, at one point saying Khashoggi had walked out of the building unharmed and later saying his death resulted from a fistfight.
And he made clear that the USA commitment to the region outpaces any presence by Russian Federation, which he said lacks essential moral principles. Turkish media have published details of his alleged torture and decapitation.
While these were some of the sharpest comments Mattis has made on the Khashoggi killing, he also said the two countries still needed to collaborate on stability in the region.