Turkish President Recep Tayyip Erdogan on Monday asked Saudi officials to prove their claim that missing journalist and Riyadh critic Jamal Khashoggi left the Saudi consulate in Istanbul.
Erdogan's comments' came after media reports said his government sought permission from Saudi authorities to search the consulate premises in Istanbul.
Khashoggi, a Washington Post contributor, vanished last Tuesday after entering the consulate to receive official documents ahead of his marriage to a Turkish woman.
"Consulate officials cannot save themselves by saying that he left the building... Don't you have a camera?" Erdogan told a news conference in Budapest.
"If he left, you have to prove it with footage. Those who ask Turkish authorities where he is should ask what happened."
Police said at the weekend that around 15 Saudis, including officials, arrived in Istanbul on two flights on Tuesday and were at the consulate at the same time as Khashoggi.
A Turkish government source told AFP at the weekend that the police believe the journalist "was killed by a team especially sent to Istanbul and who left the same day".
Riyadh vehemently denies the claim and says Khashoggi left the consulate.
Turkey on Monday sought permission to search the consulate premises, Turkish NTV broadcaster reported.
The move came after the foreign ministry summoned the Saudi ambassador for a second time Sunday over the journalist's disappearance.
A Turkish diplomat confirmed Monday that the Saudi envoy had met deputy foreign minister Sedat Onal.
"The ambassador was told that we expected full cooperation during the investigation," the source said. The ambassador was first summoned to the ministry on Wednesday.
Erdogan said Turkish police and intelligence were investigating the case.
"The airport exits and entrances are being examined. There are people who came from Saudi Arabia," he said. "The chief prosecutor's office is investigating the issue."
US President Donald Trump weighed in on the matter saying he was "concerned" about the journalist's disappearance.
"Right now, nobody knows anything about it. There are some pretty bad stories going around. I do not like it." Trump told reporters at the White House.
- 'Awful crime'-
Protesters gathered outside the Saudi consulate in Istanbul on Monday with banners reading "We will not leave without Jamal Khashoggi", demanding to know what had happened to him.
Yemeni activist Tawakkol Karman, the 2011 Nobel Peace Prize laureate, said it would be an "awful crime" if the claims of his death were true.
"Killing him is like killing us. This policy is just a terror policy. There's no difference between the state terror and other terror actions," she added.
Khashoggi went to the consulate to obtain official documents required for his marriage to Hatice Cengiz. Turkish police quickly said he never left the building as there was no security footage of his departure.
The consulate rejected claims that the journalist was killed there as "baseless".
Saudi Crown Prince Mohammed bin Salman previously told Bloomberg that Riyadh was "ready to welcome the Turkish government to go and search our premises", which is Saudi sovereign territory.
"We will allow them to enter and search and do whatever they want to do. If they ask for that, of course, we will allow them. We have nothing to hide," Prince Salman said in an interview published on Friday.
Khashoggi had been critical of some of the crown prince's policies and Riyadh's intervention in the war in Yemen in Arab and Western media.
He compared the 33-year-old prince to Russian President Vladimir Putin in a column for the Washington Post in November 2017.
"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.
- 'Devastating impact'-
A top Senate ally of Trump warned of a "devastating" impact on the US alliance with Saudi Arabia if allegations are confirmed.
Republican Senator Lindsey Graham said Riyadh must provide "honest answers" to the claims that he was murdered.
Graham said his position was shared by Bob Corker, chairman of the Senate Foreign Relations Committee, and Ben Cardin, a senior Democrat on the panel.
Saudi Arabia launched a modernisation campaign following Prince Mohammed's appointment as heir to the throne with moves such as lifting a ban on women driving.
But the ultra-conservative kingdom, which ranks 169th out of 180 on RSF's World Press Freedom Index, has been strongly criticised over its intolerance of dissent with dozens of people arrested including intellectuals and Islamic preachers.