A top Turkish official, presidential adviser Yasin Aktay, has said he believes Jamal Khashoggi's body was dissolved in acid after being cut up.
The "only logical conclusion", he said, was that those who had killed the Saudi journalist in Istanbul had destroyed his body "to leave no trace behind".
Khashoggi, a critic of Saudi rulers, was killed inside the country's consulate on 2 October.
No forensic evidence has been provided to prove his body was dissolved.
"The reason they dismembered Khashoggi's body was to dissolve his remains more easily", Mr Aktay told the Hurriyet Daily newspaper.
"Now we see that they did not only dismember his body but also vaporised it."
The claims came as Khashoggi's fiancée, Hatice Cengiz, called on world leaders to "bring the perpetrators to justice", in an editorial for five newspapers, including the Guardian and the Washington Post.
Meanwhile, reports quote Saudi Crown Prince Mohammed bin Salman as telling the US he considered Khashoggi to be a dangerous Islamist.
The reported phone call to the White House came before Saudi Arabia admitted Khashoggi had been killed.
Saudi Arabia has denied the comments were made or that its royal family was involved in the killing, and says it is "determined to find out all the facts".
Istanbul's prosecutor confirmed on Wednesday that the writer had been strangled.
During the call with President Donald Trump's son-in-law Jared Kushner and national security adviser John Bolton, Prince Mohammed said Khashoggi had been a member of the Muslim Brotherhood, a transnational Islamist organisation, the Washington Post reports.
The phone call is reported to have taken place on 9 October, a week after Khashoggi disappeared.
Prince Mohammed also reportedly urged the White House to preserve the US-Saudi alliance.
In a statement to the newspaper, Khashoggi's family denied he had been a member of the Muslim Brotherhood and said the murdered writer had himself denied this repeatedly in recent years.
"Jamal Khashoggi was not a dangerous person in any way possible. To claim otherwise would be ridiculous," the statement said.
There is still no consensus on how Khashoggi died. He entered the consulate to sort out documents for his marriage.