Turkish police said they believed Saudi journalist Jamal Khashoggi was "killed" inside the Saudi consulate in Istanbul.
Saudi officials denied the charges, saying they were "completely naked."
"The Saudi citizen Jamal Khashoggi is not in the Saudi consulate or the Saudi territories. We are looking for him and we are concerned about his disappearance," the Saudi consul in Istanbul, Mohammad al-Otaibi, told Khashoggi.
The Turkish public prosecutor opened an investigation into his disappearance.
Khashoggi, who has opposed some policies of Saudi Crown Prince Mohammed bin Salman, has disappeared since Tuesday when he entered the Saudi consulate.
"Khashoggi was killed inside the consulate," they said, quoting Turkish sources.
The sources gave no evidence or how he was killed.
What is Turkey doing?
Turkish media said the prosecution is now looking into the case closely.The two unidentified sources said Saturday that "the initial police assessment indicates that Khashoggi was killed inside the consulate."
"We believe that the murder was prepared in advance, and the body was then moved out of the consulate," one source told Reuters.
Earlier, the Turkish ruling Justice and Development Party (AKP) said the investigation would be a thorough investigation, and the Turkish government's sensitivity to the issue was "at the highest level." The party said Khashoggi's disappearance would be revealed.
Who is Jamal Khashoggi who disappeared in Turkey?
Turan Kashlajji, head of the Arab Media House in Turkey, told the New York Times that the Turkish police officers responsible for guarding the consulate checked their cameras and did not see the journalist leave on his foot. But he said diplomatic vehicles were seen moving inside and outside the consulate.
On Wednesday, the Turkish Foreign Ministry summoned the Saudi ambassador and asked him for clarifications about Khashoggi's disappearance.
Mark Lewin, the BBC's Turkey correspondent, says the mystery of the case threatens to deepen tensions in relations between Turkey and Saudi Arabia.
He added that Turkey provided great support to Qatar under the embargo imposed by Saudi Arabia and other Arab countries, and the rapprochement between Turkey and Iran has angered Riyadh.
What did Saudi Arabia say?
"He (Khashoggi) is a Saudi citizen, they are keen to know what happened to him, and we will continue our contacts with the Turkish government to find out what happened to Gamal there," Prince Mohammad bin Salman told Bloomberg.
"As far as I know he entered the consulate and got out of it a few minutes or an hour later, I'm not sure, we're investigating the case through the State Department to see exactly what happened at the time."
"The consulate is sovereign land, but we will allow them (Turks) to enter, search and do what they want, if they ask for it, of course, we will allow them, we have nothing to hide," Salman said.
Asked if Khashoggi had faced charges in Saudi Arabia, the prince said his country would first want to know where he had disappeared.
