The Turkish president says a 15-person team travelled from Riyadh to kill Khashoggi, who had criticized Saudi Arabia's powerful Crown Prince Mohammad bin Salman, after he entered the Saudi consulate on October 2.
"The victim's body was dismembered and destroyed following his death by suffocation".
Turkish President Recep Tayyip Erdogan said Tuesday the investigation needs to be completed swiftly. After this, the statement alleges, Saudi officials proceeded with dismembering Khashoggi to secretly transport his body and cover up the killing.
The fiancée of Saudi journalist Jamal Khashoggi has said Saudi authorities are responsible for his slaying, and the kingdom should give more details so that those responsible can be brought to justice.
"The Saudi officials seemed primarily interested in finding out what evidence the Turkish authorities had against the perpetrators", the official told AFP on the condition of anonymity.
The case has sorely strained relations between Saudi Arabia and the West, and has fuelled worldwide debate about arms deliveries to the ultra-conservative kingdom.More news: U.S. grants Iran sanctions waivers to eight countries including India
Mr Khashoggi entered the consulate in Istanbul on October 2 to get the needed paperwork to marry his partner.
Defense Secretary Jim Mattis said he met with Saudi Arabia's foreign minister during an global conference and urged a full and complete investigation into the killing of writer Jamal Khashoggi.
Saudi hit squadCleaning personnel wait to enter Saudi Arabia's Consulate in Istanbul, Monday, Oct. 15, 2018.
The head of the Saudi investigation, Attorney General Sheikh Saud al-Mojeb, last week acknowledged that the killing was "premeditated", based on Turkish evidence.
Mojeb left Turkey on Wednesday evening after a three-day visit during which he also held talks at the offices of Turkey's National Intelligence Agency (MIT).
Khashoggi was a Washington Post columnist and outspoken critic of the Saudi leadership.