Turkish police believe that a missing Washington Post contributor who disappeared after entering the Saudi consulate in Istanbul was murdered.

Reuters reports that two Turkish police sources say authorities now believe Jamal Khashoggi was murdered sometime after he entered the consulate four days ago.

"The initial assessment of the Turkish police is that Mr. Khashoggi has been killed at the consulate of Saudi Arabia in Istanbul," one Turkish law enforcement official said.

"We believe that the murder was premeditated and the body was subsequently moved out of the consulate," the official added.

The remarks came hours after Turkey's government announced an investigation into Khashoggi's sudden disappearance.

A request for comment to the Saudi Embassy in Washington, D.C., from The Hill was not immediately answered.

Khashoggi was living in self-imposed exile in the U.S. for a year because of his frequent criticism of Saudi Arabia's government and royal family.

In previous statements, Saudi officials welcomed an investigation into Khashoggi's disappearance and invited a search of the country's consulate in Istanbul.

"We are ready to welcome the Turkish government to go and search our premises," Saudi Crown Prince Mohammed bin Salman said in an interview with Bloomberg on Friday.

"We will allow them to enter and search and do whatever they want to do," he added. "We have nothing to hide."