The killing of journalist Jamal Khashoggi was planned days in advance, Turkish President Recep Tayyip Erdogan has told MPs from his ruling party.
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 had ordered the operation.
The Saudi kingdom has provided conflicting accounts of what happened to Khashoggi, a US resident and 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.
Mr Erdogan’s address coincided with the start of an investment conference in Saudi Arabia that has been overshadowed by the Khashoggi case. Dozens of government and business leaders have pulled out, but Crown Prince Mohammed bin Salman appeared at the event on Tuesday.
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. CIA director Gina Haspel has been sent to Turkey to review the matter.
What did the Turkish president say happened?
Fifteen Saudi nationals, Mr Erdogan said, arrived in Istanbul in three teams, 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 searched last week 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 the arrival of Khashoggi, who was visiting to obtain documents for his forthcoming marriage.
A man who looked like Khashoggi, wearing his outfit, glasses and a fake beard, was among a group who left the consulate the same day as the killing, the president added.
On Monday, CNN broadcast images appearing to show that Saudi operative leaving the consulate.
President Erdogan confirmed 18 people had been arrested in Saudi Arabia over the case.
He told MPs from his ruling AK party the 18 should “be tried in Istanbul”, adding that “all those who played a role in the murder” would be punished.
What did he say about the Saudis?
Mr Erdogan called for an independent commission to be set up but said he was confident in King Salman’s full co-operation.
He did not mention the crown prince, widely seen as the most powerful figure in the kingdom. Many believe he ordered the killing, although the Saudis deny this.
BBC security correspondent Frank Gardner says Mr Erdogan’s speech was notable as much for what it left out as for what it left in.
There was no mention of the much-discussed audio tape from inside the Saudi consulate which Turkish media say reveals gruesome details of the murder.
Trailed as something that would expose “the naked truth”, the speech fell well short of many people’s expectations, our correspondent says.
Where do the Saudis stand?
King Salman chaired a cabinet meeting on Tuesday, after which a statement said that Saudi Arabia would hold to account those responsible for the killing, whoever they might be.
State media also said the king and the crown prince had held a meeting in Riyadh with members of the Khashoggi family, including Khashoggi’s son, Salah bin Jamal.
Mr Erdogan also spoke to family members by phone on Tuesday, offering condolences and saying he would do all he could to solve the murder.
Saudi Arabia has given conflicting accounts up to now, initially saying Khashoggi had left the building alive, then later saying that he had been killed in a “fist-fight” inside the consulate.
On Sunday, the Saudi foreign minister acknowledged Khashoggi had been murdered but said the 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 news agency 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 an organisation, 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 as 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.
Who is at the investment conference?
BBC’s Sebastian Usher in Riyadh
There’s an odd mixture of unreality and hard-faced pragmatism here.
Attendees say they’re here to stay with the opportunities Saudi Arabia provides for the long haul – however much pressure may be building in the short term. But that means that the urgency and outrage over the killing of Jamal Khashoggi that is fuelling the news outside is absent here.
As President Erdogan was delivering his explosive speech, the conference here announced $ 50bn (£38.5bn) of investment in 12 mega-deals. The contracts were signed with a flourish by a host of foreign CEOs with their Saudi partners to the applause of the audience.
It was no doubt intended as a resounding vote of confidence in the vision of Saudi Arabia’s future laid out by Crown Prince Mohammed bin Salman. But that future and those investments could still turn sour, despite the mood of optimism and self-approbation exhibited here.