Istanbul, Turkey (CNN) Turkey's President Recep Tayyip Erdogan says he is personally "chasing" the investigation into prominent Saudi journalist Jamal Khashoggi who went missing after entering the Saudi Arabian Consulate in Istanbul last week.

The President's comments came after unnamed Turkish officials told the The Washington Post and Reuters on Saturday that Khashoggi was killed inside the consulate. The officials have so far provided no evidence or details on how they arrived at this conclusion.

"I am following it up as the President of the Turkish Republic," Erdogan told reporters in Ankara on Sunday, while also confirming that he had known Khashoggi for some time and considered him a friend.

"I am chasing. We will of course share the result with the world," Erdogan added. "All the footage of entrance or exit of the embassy is under investigation."

Khashoggi, a Washington Post writer and outspoken critic of Saudi Crown Prince Mohammed bin Salman's leadership, entered the consulate Tuesday to obtain documents for his upcoming marriage while his Turkish fiancée waited outside. But his fiancée says she never saw him re-emerge.

Yasin Aktay, a political adviser to Erdogan, told CNN Sunday he too believes there is a strong possibility that Khashoggi was killed inside the Saudi consulate.

"I personally think the possibility of him being killed is stronger than other possibilities, although I do not want to accept it. Because if he was alive, Saudis would provide evidence that he is alive," Aktay told CNN during a telephone interview in Istanbul.

"If he is not in the consulate and if he did not leave through the normal ways, he might have left sedated or left in pieces."

Saudi Arabia has strenuously denied any involvement in Khashoggi's disappearance, calling the claims "false." A Saudi official said Khashoggi left the consulate shortly after he visited. The Saudis did not, however, release any surveillance footage or other evidence.

As demands for answers grew, the consulate gave journalists a tour of the six-story building in an effort to prove Khashoggi was not inside. Reuters said that a consulate official gave their journalists a tour of each room, even opening up cupboards and filing cabinets. No sign of him was found.

A statement released on Sunday on behalf of Khashoggi's family in Saudi Arabia accused the media of politicizing his disappearance.

"We trust the government and the actions taken by it and all the efforts being made in the case of Jamal Khashoggi. There's coordination with the government and the embassy in Ankara," read the statement.

"We know the objectives behind electronic media and frenzied news outlets that attack our country for negative purposes. We tell these people to remain silent as their purposes and intentions have failed."

Khashoggi's disappearance comes amid a wave of arrests of Saudi critics, allegedly steered by the Crown Prince. The crackdowns have targeted clerics, journalists, academics and activists, some of whom were detained outside Saudi Arabia.

Aktay, who is also an adviser to the ruling AK Party, told CNN that said the Turkish government is not "ignoring any piece of evidence," and said the Saudis are not "sharing any convincing explanations on what happened inside the building."

"This is an attack to Turkey's image. All people who enter Turkey under visa are under Turkey's protection," Aktay said. "Turkey is holding Saudi Arabia accountable."

Saudis arrived on planes

Erdogan suggested Sunday that the Turkish investigation included the arrival of a number of Saudi officials in Istanbul.

Fifteen Saudis, including several officials, arrived in the city on two planes and visited the consulate while Khashoggi was being held, the official Anadolu agency reported quoting Turkish police.

"The arrival at the airport, the departure, is under investigation," Erdogan said.

The President did not directly address reports that Khashoggi had been killed.

But he did say that "Jamal is a journalist who I have known for long time, a friend. Therefore my expectation is still based on good intentions.

A friend of Khashoggi, Turan Kislakci, who is also the head of the Turkish-Arab Media Association, told CNN that Turkish officials had called him and "offered their condolences and told us to be ready for a funeral."

"Today we were meant to meet," Kislakci said Sunday of his missing friend.

"It should have been today that he had his (official) papers -- this week -- either today or next Sunday he was planning to get married. But this never happened," said Kislakci, adding that Khashoggi's friends were preparing to hold a funeral in absentia in the coming days.

Turkish police have reportedly examined surveillance footage from the area and said there was no sign of Khashoggi leaving the consulate, Kislakci said.

Activist Tawakkol Karman holds a picture of missing journalist Jamal Khashoggi during a demonstration in front of the Saudi Arabian consulate in Istanbul on Friday.

Two senior US administration officials told CNN Sunday that although Washington is not commenting publicly, and has no information confirming the Turkish claims, the administration is quietly working across several agencies, seeking answers about Khashoggi's whereabouts and talking to senior Saudi officials.

Earlier, a spokesman with the US State Department told CNN the agency was monitoring the situation but could not confirm the reports of Khashoggi's death.

On Thursday, Virginia congressman Gerry Connolly tweeted his concern for Khashoggi -- who lives in Virginia -- calling on "the Saudi and Turkish governments to ensure his safety and freedom."

I am deeply concerned by reports that Jamal Khashoggi, renowned journalist and VA resident, has disappeared after visiting the Saudi consulate in Istanbul. I call on the Saudi and Turkish governments to ensure his safety and freedom. My office is following this matter closely. — Gerry Connolly (@GerryConnolly) October 4, 2018

Washington Post publishes blank column

Khashoggi, known in part for his interviews with terror mastermind Osama bin Laden, was a Saudi royal court insider before he left Saudi Arabia in 2017 for Washington. He began to contribute opinion pieces to The Washington Post that were critical of bin Salman's policies, including his consolidation of power. He was named a contributing writer at the Post in January.

In Friday's edition, the Post printed a blank space where Khashoggi's column would have been.

Khashoggi said the Saudi government had ordered him to stop using Twitter after he sent a tweet cautioning against the leadership's enthusiasm about Donald Trump, then the US president-elect.

"So I spent six months silent, reflecting on the state of my country and the stark choices before me. It was painful for me several years ago when several friends were arrested. I said nothing. I didn't want to lose my job or my freedom. I worried about my family," he wrote in a September 2017 Washington Post opinion piece titled "Saudi Arabia wasn't always this repressive. Now it's unbearable."

"I have made a different choice now. I have left my home, my family and my job, and I am raising my voice. To do otherwise would betray those who languish in prison."