Saudi Arabia's King Salman on Monday ordered an internal probe into the unexplained disappearance of prominent journalist Jamal Khashoggi as a joint Turkish-Saudi team was set to search the Saudi consulate in Istanbul where he was last seen on Oct. 2.

A Turkish diplomatic source said investigators would inspect the consulate on Monday afternoon, following delays last week when the two countries agreed to work together to find out what happened to Khashoggi, a critic of the Kingdom's policies.

"The King has ordered the Public Prosecutor to open an internal investigation into the Khashoggi matter based on the info from the joint team in Istanbul," a Saudi official, not authorized to speak publicly, told Reuters.

Asked when the public prosecutor could make an announcement about the investigation, the official said: "He was instructed to work quickly."

Khashoggi, a U.S. resident, disappeared after entering the consulate to get marriage documents. Turkey believes he was murdered and his body removed, while Saudi Arabia has denied the allegations.