A Turkish diplomatic source confirmed on Monday that the Saudi envoy had met deputy foreign minister Sedat Onal.
The board said Saudi Arabia has to identify the 15 officials who were at the consulate and exactly what happened inside. The ambassador was first summoned to the ministry on Wednesday.
The whistleblower organization tweeted that no British newspaper had led their Monday front pages with news about Khashoggi's suspected murder despite the fact that news agencies like the Associated Press and Reuters were all reporting on the story - and suggested that the lack of interest from the United Kingdom papers was due to the fact that they "all take Saudi money".
However, he was sacked from his post as an editor at Al-Watan, a liberal paper founded after the 9/11 terror attacks, just two months after he took the job in 2003. They included a friend of Khashoggi's who had just returned from a trip to the U.S.as part of an official Saudi delegation. Khashoggi had left his mobile phone with her, and told her to call Turkish authorities if he did not return.
Saudi Arabia said the allegations were "baseless".
The Saudi Crown Prince refuted the claims later in an interview during which he said Turkey can search the kingdom's consulate in Istanbul for the Saudi journalist, saying: "We have nothing to hide". "But shouldn't we aspire to allow the marketplace of ideas to be open?"
Prince Mohammed downplayed any apparent rift with the USA leader and said relations between the two allies remains strong.
The Saudi writer spent previous year in the U.S in self-imposed exile, after he fled the kingdom amid a crackdown on intellectuals and activists who criticized the policies of Crown Prince Mohammed bin Salman. Mr Khashoggi, 59, has more than 1.6 million Twitter followers and has written for the Washington Post opinion section.
"As of now, I would say Mohammed bin Salman is acting like Putin".
"He is imposing very selective justice. The crackdown on even the most constructive criticism - the demand for complete loyalty with a significant ´or else´ - remains a serious challenge to the crown prince´s desire to be seen as a modern, enlightened leader", he wrote.
A Turkish official separately told The Associated Press that authorities believe Khashoggi was killed at the Saudi Consulate, while another said it was a "high probability" that Khashoggi's body was taken away.
"We hope to have results very quickly".
Erdogan said that CCTV footage of entrances and exits at the consulate and the airport in Istanbul were being studied by the police.
Saudi Arabia, the UAE, Bahrain and Egypt cut ties with Doha in June 2017 over allegations it supports extremists and is cosying up to arch-rival Iran and Islamist group the Muslim Brotherhood.
In his initial comments on Sunday, Erdogan struck a cautious tone with regards to the circumstances surrounding Khashoggi's disappearence. It could cause the USA and Europe to reevaluate their relationships with Saudi Arabia, and with Turkish officials so enraged by this, it could trigger a more serious response.
The Trump family - in particular the president's son-in-law, Jared Kushner - has established a close bond with Saudi crown prince Mohammed bin Salman.