And while the authorities here are so far not providing evidence to back it up, it's inconceivable that such a claim would have been made without firm grounds.
A spokesman for Turkey's ruling AK Party said Saturday that authorities would finally uncover Khashoggi's whereabouts.
His Turkish fiancée Hatice Cengiz, who was waiting outside for him on Tuesday, says he never re-emerged.
"I would like to confirm that".More news: Trump NYT tax report 'false attack': White House
After several of his friends were arrested, his column was cancelled by the al-Hayat newspaper and he was allegedly warned to stop tweeting, Mr Khashoggi left Saudi Arabia for the U.S., from where he wrote opinion pieces for the Washington Post and continued to appear on Arab and Western TV channels.
Ankara alleges that Khashoggi, 59, a prominent contributor to the Washington Post who lived in a self-imposed exile in the United States, is still inside the consulate building. The official spoke on the condition of anonymity because the official was not authorized to discuss the case on the record.
The Turkish source said Turkish officials were trying to identify them.
Saturday evening, the Post wrote that "the killing, if confirmed, would mark a stunning escalation of Saudi Arabia's effort to silence dissent". Human and women's rights activists, intellectuals and clerics have been arrested - meanwhile, Saudi Arabia is waging a war in Yemen that has triggered a humanitarian crisis.
The Washington Post's editorial page editor Fred Hiatt said in a statement: "If the reports of Jamal's murder are true, it is a monstrous and unfathomable act".
The Committee to Protect Journalists said it was alarmed by reports Khashoggi may have been killed inside the consulate.More news: Hubble data hints at first ever moon outside our moon
Saudi Arabia, which ranks 169th out of 180 on the World Press Freedom Index issued by Reporters Without Borders (RSF), has launched a modernisation campaign since Prince Mohammed's appointment as heir to the throne. "We have been enormously proud to publish his writings".
A Saudi source at the consulate denied that Khashoggi had been killed at the mission and said in a statement that the accusations were baseless.
The United States is seeking more information, a State Department said.
Rather, he has always been a pillar of the Saudi establishment who was close to its ruling circles for decades, had worked as an editor at Saudi news outlets and had been an adviser to a former Saudi intelligence chief.
Turan Kislakci, a friend who heads the Arab Turkish Media Association, said that Khashoggi received assurances from Saudi officials before his visit that he could enter safely.
A senior Turkish police source told MEE that Khashoggi had been "brutally tortured, killed and cut into pieces".More news: Chicago police officer jailed after guilty verdicts