A man places a poster of missing Saudi writer Jamal Khashoggi, on a barrier that blocks the road leading to the Saudi Arabia consulate in Istanbul, as people gather in his support, Friday, Oct. 5, 2018. "Deeply troubled to hear reports about Saudi Arabian journalist Jamal Khashoggi".
Khashoggi, 59, has had a long career as a senior journalist in Saudi Arabia and also as an adviser to top officials.
Riyadh has denied Khashoggi was killed or detained on its Istanbul premises, and claims that the veteran journalist left the consulate shortly after entering.
Turkey's Foreign Ministry said a search would be conducted there, while the United Nations human rights office urged both countries to investigate Khashoggi's disappearance.
"Jamal has many friends in the Kingdom, including myself", Khalid wrote.
Tuesday's statement from the Turkish foreign ministry's spokesman, Hami Aksoy, said Saudi authorities have notified Ankara that they were "open to cooperation" and would allow the consulate building to be searched.
The Post's image showed Jamal Khashoggi walking into the Saudi Consulate in Istanbul a week ago.
Turkish President Recep Tayyip Erdogan said on Sunday he was awaiting the results of an investigation into Khashoggi's disappearance and maintains positive expectations on his fate.
Erdogan said the Saudi consulate should have surveillance cameras and should be able to show the video of Khashoggi leaving the building.
But it was not immediately clear whether Turkish officials were granted access to the consulate after Monday's request.
Two Turkish sources told Reuters Turkish authorities believe Khashoggi was deliberately killed inside the consulate, a view echoed by one of Erdogan's advisers, Yasin Aktay, who is also a friend of the Saudi journalist.
BBC Newshour interviewed the journalist just three days before his visit to the consulate, and in an off-air conversation asked if he would ever return to his home country. "If he's in Saudi Arabia, I would know that".
Turkey has an extensive system of motorway cameras that are regularly used to provide evidence in criminal probes.
"It's very, very sad for us that this happened in our country", the Turkish president said.
A member of the Saudi elite, he had remained in exile in the USA for much of the past year, from where he wrote columns for The Washington Post critiquing aspects of the Kingdom's reform programme.
Khashoggi was right about Saudi repression.
Fusun Arsava, an global law professor at Ankara's Atilim University, told Al-Monitor that even if reports of Khashoggi's murder were true, that would be extremely hard for the Turkish authorities to prove.
The New York Times account says its sources report the Saudis "had arrived to silence Mr. Khashoggi, but that it was not clear if the plan had been to bring him back to Saudi Arabia alive, and something went wrong, or if the intention was to kill him there".