Khashoggi, a noted critic of Saudi Arabia's Crown Prince Mohammed bin Salman who wrote for the Washington Post, was killed in Saudi Arabia's consulate in Turkey on October 2.

After making numerous contradictory statements about Khashoggi's fate, Riyadh said he had been killed and his body dismembered when negotiations to persuade him to return to Saudi Arabia failed.

Turkey has previously said it was working with other countries on the Khashoggi investigation, and has accused Saudi Arabia of not fully cooperating.

Cavusoglu said in a speech that some Western countries were trying to cover up Khashoggi's murder, adding that Turkey had made preparations to launch an international investigation on the matter, state media said.

"There are Western countries trying to cover this case up. I know the reasons. We know and see what sorts of deals are made. We see how those who spoke of freedom of press are now covering this up after seeing money,"he said.

Despite a joint investigation with Saudi officials in Istanbul, the whereabouts of Khashoggi's remains are still unknown.

Turkish President Tayyip Erdogan has said Khashoggi's killing was ordered by the highest level of Saudi leadership, but Riyadh has rejected accusations that the prince was involved.

Saudi prosecutors are seeking the death penalty for five of the 11 suspects detained over the murder, which has caused international outrage and damaged the reputation of the 33-year old crown prince.

Australian Associated Press