Turkish President Recep Tayyip Erdogan says a Saudi prosecutor is due to visit Istanbul on Sunday to meet a Turkish counterpart as part of an ongoing probe into the killing of Saudi dissident journalist Jamal Khashoggi.

"[Saudi Arabia] are sending a chief prosecutor to Turkey on Sunday. He will meet our chief prosecutor in Istanbul," Erdogan told a meeting of his ruling Justice and Development Party (AKP) in Ankara on Friday.

Turkey has taken statements from 38 employees at Saudi Arabia's consulate in Istanbul, while another five employees were still to be questioned, state news agency Anadolu reported on Thursday.

Khashoggi, a sharp critic of the powerful Saudi Crown Prince Mohammed bin Salman, has not been seen since he walked into the consulate on October 2 in order to get paperwork done to marry a Turkish woman.

After weeks of denials, the Saudis have acknowledged that Khashoggi was killed in the consulate. Saudi Arabia's chief prosecutor said on Thursday that the murder was premeditated.