Turkish President Recep Tayyip Erdogan vowed on Sunday to reveal within days the "naked truth" over the death of dissident journalist Jamal Khashoggi inside the Saudi consulate in Istanbul.

US President Donald Trump has refused to take a harsh stance against Saudi Crown Prince Mohammed bin Salman, whom the US leader has defended as an invaluable trade partner even as world powers demand answers over the October 2 killing of Khashoggi, a vocal critic and Washington Post columnist who fell out of favour with Riyadh.

But the Saudi foreign minister, Adel al-Jubeir, insisted on Sunday that Prince Mohammed was "not aware" of the killing and that the kingdom does not know where the body is.

Erdogan, whose ties to Saudi Arabia appear to have further soured over the Khashoggi case, said he would reveal the findings of his country's investigation into the killing in the coming days.

The Turkish leader's statement came one day after Saudi authorities conceded Khashoggi had been killed inside their diplomatic compound in Istanbul.

"We are looking for justice here and this will be revealed in all its naked truth, not through some ordinary steps but in all its naked truth," Erdogan told a rally in Istanbul.

Erdogan is expected to make a full statement to his party's MPs on Tuesday.

Turkish officials have said they believe that 15 Saudi men who arrived in Istanbul on two flights on October 2 were connected to his death.

Riyadh reacted by claiming one of the 15 had died in a car accident years ago.

Saudi officials originally said Khashoggi, who entered the diplomatic mission on October 2, had left unharmed, before announcing Friday he was killed inside the building in what they described as an altercation.

The kingdom has since admitted Khashoggi died in a "brawl" inside the consulate and said it has fired five top officials and arrested 18 others in an investigation into the killing.

- Turkey vs. Trump -

Khashoggi, who would have been 60 this month, sought refuge in the United States after he fled his native Saudi Arabia following the 2017 appointment of strongman Mohammed bin Salman as heir to the throne.

The journalist, who has espoused both Islamist and liberal views throughout his decades-long career in the press, was engaged to a Turkish citizen.

His killing has further soured relations between Saudi Arabia and Turkey, already at loggerheads over Qatar, with which Riyadh cut ties in 2017 and to which Ankara has deployed aid and troops.

Turkish officials now accuse Riyadh of carrying out a state-sponsored killing and dismembering the body, with pro-government media in Turkey reporting the existence of video and audio evidence to back those claims. (AFP)