The killing of journalist Jamal Khashoggi was planned days in advance, Turkish President Recep Tayyip Erdogan has told MPs from his ruling party, reports BBC.
He said Turkey had strong evidence Khashoggi was killed in a premeditated and "savage" murder at the Saudi consulate in Istanbul on 2 October.
He also called for the suspects to be tried in Istanbul.
He demanded Saudi Arabia provide answers about where Khashoggi's body was, and who ordered the operation.
The Saudi kingdom has provided conflicting accounts of what happened to the Washington Post contributor. After weeks of maintaining he was still alive, the authorities now say the 59-year-old was killed in a rogue operation.
Tuesday's address by President Erdogan coincided with the start of an investment conference in Saudi Arabia that has been overshadowed by the Khashoggi case, with dozens of government and business leaders pulling out.
Many world leaders have condemned the murder of the prominent Saudi critic and demanded a full investigation.
US President Donald Trump says he is not satisfied with the Saudi explanation but he has also highlighted the kingdom's importance as a US ally.
What did the Turkish president say happened?
President Erdogan said three teams of 15 Saudi nationals had arrived in Istanbul on separate flights in the days and hours leading up to the murder.
A day before the killing, he said, some members from the group travelled to Belgrad forest, near the consulate - an area which was last week searched by Turkish police looking for the body.
He also described how the team had removed the hard drives from the consulate's surveillance camera system prior to Khashoggi's arrival - who was visiting to obtain documents for his forthcoming marriage.
A man who looked like Khashoggi, wearing his outfit, glasses and beard, was among the group who left the consulate the same day as the killing, the president added.
On Monday, CNN broadcast images appearing to show a Saudi operative leaving the consulate in Khashoggi's clothes, wearing a fake beard and glasses.
President Erdogan confirmed that 18 people had been arrested in Saudi Arabia over the case. However, he has not released any details of the evidence gathered.
He made no mention of any audio or video recordings reported by Turkish media in the days following the journalist's disappearance.
"My demand is that 18 people be tried in Istanbul," he told MPs from his ruling AK party, adding that "all those who played a role in the murder" would be punished.
He said the suspects included the 15 Saudi officials identified flying to Istanbul ahead of the killing, as well as three consular officials.
What did he say about the Saudis?
Mr Erdogan called for an independent commission to be set up to look into the case, but said he was confident of King Salman's full co-operation.
He did not mention the Crown Prince Mohammed bin Salman, widely seen as the most powerful figure in the kingdom and who many believe ordered the killing.
For a president not shy of confrontation, this could be another attempt to preserve the diplomatic relationship with Saudi Arabia or a result of pressure from Riyadh or Washington to hold back, says the BBC's Mark Lowen in Istanbul.
The Turkish president had promised to reveal the "naked truth" about the killing, but his speech gave barely more detail than we knew, our correspondent added.
Where do the Saudis stand?
Saudi Arabia has given conflicting accounts, initially saying Khashoggi left the building alive, then later saying that he had been killed in a "fist-fight" inside the consulate.
On Sunday, Saudi Arabia's foreign minister acknowledged Khashoggi had been murdered, but said the Saudi leadership had not been aware of the "rogue operation".
"The individuals who did this did this outside the scope of their authority," Foreign Minister Adel al-Jubeir told Fox News. "There obviously was a tremendous mistake made, and what compounded the mistake was the attempt to try to cover up."
He said that Saudi Arabia did not know where the body was.
An unnamed Saudi official told Reuters on Sunday that Khashoggi had died in a chokehold after resisting attempts to return him to Saudi Arabia. His body was then rolled in a rug and given to a local "co-operator" to dispose of.
President Erdogan demanded in his speech on Tuesday for this individual's identity to be revealed.
In addition to the arrests, the Saudis say they have sacked two of the crown prince's aides and set up a body, under his leadership, to reform the intelligence agency over the killing.
According to Reuters news agency, quoting Turkish and Arabic intelligence sources, one of the sacked aides appeared via Skype during Khashoggi's questioning. Saud al-Qahtani was quoted giving the instructions "bring me the head of the dog", after the two men traded insults.
The sources say President Erdogan has a copy of the Skype audio, but is refusing to hand it over to the US.
Is anyone attending the investment conference?
At least 40 attendees have withdrawn from the Future Investment Initiative, a conference dubbed "Davos in the Desert" that began in Riyadh on Tuesday.
The big names may have pulled out but hundreds are still attending - in some cases representing the very companies whose bosses decided it was no longer expedient for them to attend, the BBC's Arab affairs editor Sebastian Usher reports from Riyadh.
The talk among delegates is of pragmatism, that there is a big future at stake in Saudi Arabia and this obstacle - however shocking and overwhelming - will eventually be overcome, he adds.
Saudi Arabia has come under increased pressure from its Western allies over the Khashoggi murder, with Germany halting arms exports and Canada threatening to cancel a multi-billion-dollar defence contract.
The kingdom still has the support of some of its regional allies, including Kuwait and Eg
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