Turkish police have concluded that prominent Saudi journalist Jamal Khashoggi was murdered inside the Saudi mission in Istanbul after going missing Tuesday, an unnamed government official has said.

Turkish officials have said they believe Khashoggi, 59, a critic of the Saudi leadership and a contributor to The Washington Post's Global Opinions section, was killed by a team of 15 Saudis flown in specifically to carry out the attack. He left the country a year ago for the United States fearing retribution from the kingdom which has recently witnessed widespread crackdown on dissent. "God willing, we will not face an undesired situation", he told reporters, avoiding confirming claims that the journalist was killed.

An advisor to Turkey's president has vowed that the country will prosecute all those involved in the suspected kidnapping or murder of a dissident Saudi journalist in Riyadh's consulate in Istanbul, even if it involves the Saudi consul himself. The consulate insists Khashoggi left its premises, contradicting Turkish officials.

"Everything is being inspected, especially entries and exits out of Istanbul, the airport", he said.

But if Khashoggi is dead, the Saudi government certainly had a motive to kill him.

"His friends had warned him, 'Don't go there, it is not safe, ' but he said they could not do anything to him in Turkey", said Aktay.

Image copyright AFP Image caption The Saudi consulate said Khashoggi left after completing paperwork Who is Jamal Khashoggi?

Khashoggi, a former Saudi government adviser, had been living in self-imposed exile in the United States since previous year fearing possible arrest.

Turkish investigators believe that Khashoggi, 59, was killed shortly after he entered and his body was later removed from the premises, a US official and sources close to the investigation said. Its passengers went straight to the consulate and then left in the evening for Egypt.

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"The Saudis are saying we can come investigate, but they have of course disposed of the body", he said, adding that he believed Saudi statements about a lack of footage from security cameras were insincere. "We want to swiftly get results", he said, adding without explanation: "My expectation is still positive".

Over the past year, he has written columns for newspapers including the Washington Post criticizing Saudi policies toward Qatar and Canada, the war in Yemen and a crackdown on dissent which has seen dozens of people detained.

While living in Saudi Arabia, Khashoggi was told to stop writing or posting on Twitter, where he has more than 1.6 million followers.

"Consulate officials can't save themselves by saying, 'He left here.' And relevant authorities are obligated to provide proof of this claim", Erdogan said during a visit to Hungary.

What have both countries said?

. "State Department senior officials have spoken with the Kingdom of Saudi Arabia through diplomatic channels about this matter", he said.

The source also stated that a security delegation of Saudi investigators arrived in Istanbul on Saturday based upon a request by the Saudi government, and the acceptance of the Turkish authorities.

Turkey's foreign ministry on Wednesday summoned Saudi Arabia's ambassador over the issue.

Human rights activists hold pictures of Saudi journalist Jamal Khashoggi during a protest outside the Saudi Consulate in Istanbul, Turkey Oct. 9, 2018.

"And that happened", the crown prince told Bloomberg on Friday in a wide-ranging interview.