Turkey "will never allow a cover-up" over the death of Jamal Khashoggi, a senior official in the country's ruling party has said.
It comes after Saudi Arabia dramatically changed its story and claimed the journalist had died at its consulate in Istanbul after a fist fight spiralled out of control.
Numan Kurtulmus, deputy head of the Justice and Development Party, said a "conclusive result" of Turkey's investigation was close and would be shared with the world.
There has been no word from Saudi authorities on what was done with Mr Khashoggi's body.
The search for his remains is focused on a forest near Istanbul and the coastal city of Yalova, with officials saying they are looking at CCTV to trace the movements of vehicles that went in and out of the consulate on the day Mr Khashoggi disappeared.
:: Who was Jamal Khashoggi?
An official Saudi statement said "discussions" with the 59-year-old "did not go as required and developed in a negative way, leading to a fight and a quarrel".
It expressed "deep regret" and said "the brawl aggravated to lead to his death and their attempt to conceal and cover what happened".
Authorities - including the crown prince - had previously said that Mr Khashoggi walked out of the consulate not long after his appointment on 2 October.
Eighteen Saudis have been arrested, according to Saudi Arabia's statement, while two senior officials have also been sacked: deputy intelligence chief Ahmed El Assiri and royal court adviser Saud Al Qahtani.
Critics claim they are being used to deflect blame from the country's de-facto ruler Crown Prince Mohammed Bin Salman, who is widely believed to tightly control all major decisions in the kingdom.
:: How journalist met his death
The Saudi explanation contrasts with details of the case that Turkish officials have anonymously leaked to the media.
They say it was a premeditated murder, with Mr Khashoggi tortured and having his fingers cut off before his body was dismembered on an office table by a forensic doctor.
According to Turkish media reports, authorities have audio of the alleged murder.
Germany's foreign minister Heiko Maas has said Germany should not approve arms sales to Saudi Arabia before a investigation into the death is completed.
German Chancellor Angela Merkel said: "We condemn this act in the strongest terms.
"We expect transparency from Saudi Arabia about the circumstances of his death... the information available out events in the Istanbul consulate is inadequate."
US President Donald Trump initially said he found the Saudi explanation "credible", but on Saturday said he was not satisfied with the account of events.
The UK's Foreign Office said it was "considering the Saudi report and our next steps", while a UN spokesman said secretary-general Antonio Guterres was "deeply troubled" by the death.
France has also condemned the killing and the EU's Federica Mogherini said the circumstances were "deeply troubling".
Regional allies have struck a different tone, with Bahrain, the United Arab Emirates, Yemen and Egypt praising Saudi Arabia's King Salman for the way the investigation into the death was handled.
Amnesty International has urged Saudi Arabia to "immediately produce" Mr Khashoggi's body so a proper post-mortem examination can be performed.
Concerns for Mr Khashoggi began after his fiancee, Hatice Cengiz, raised the alarm when he did not come out of the consulate after going in to get papers so they could marry.
She tweeted that her heart was "full of sorrow" at hearing confirmation of his death.
Turkish sources have said he was killed by a 15-man "hit squad" which flew in by private jet and left the same day.
Pro-government media in the country published CCTV of men outside the consulate and at the airport, with one said to be a bodyguard and regular member of Crown Prince Mohammed bin Salman's entourage.
Major businesses and some politicians, including the UK's trade secretary, have pulled out of a large investment summit in Saudi Arabia's capital, Riyadh, next week.
Mr Khashoggi, a Washington Post columnist, fled Saudi Arabia for Washington in September 2017 - months after Prince Mohammed was appointed heir to the throne.
He had been criticised by Saudi authorities for being too progressive and he had described Prince Mohammed as a "brash and abrasive young innovator" - and even said he was "acting like Putin".
The prince is popular among many in his country, particularly the young, for his social reforms such as allowing women to drive, allowing more entertainment events and weakening the power of the religious police.