Mr Khashoggi, a Saudi national, went missing after visiting the Saudi consulate in Istanbul on Tuesday.
A Turkish official told the BBC that initial investigations indicated he was murdered there.
Saudi Arabia has denied the accusations, saying it is "working to search for him".
The Washington Post said it would be a "monstrous and unfathomable act" if he had been killed.
The BBC's Istanbul correspondent, Mark Lowen, said it would plunge Turkish-Saudi relations into an unprecedented crisis.
Turkish officials have opened an investigation and have been speaking to the media on condition of anonymity.
The deputy chairman of Turkey's ruling AK Party told broadcaster CNN Turk there was concrete evidence, according to Reuters news agency, but none has yet been presented.
When was he last seen?
Jamal Khashoggi is a high-profile critic of Saudi Arabia's Crown Prince Mohammed bin Salman. He has more than 1.6 million Twitter followers and has written for the Washington Post opinion section.
On Tuesday, he went to the consulate to obtain a document certifying he had divorced his ex-wife, so that he could marry his Turkish fiancée, Hatice Cengiz.
Ms Cengiz said she waited outside for 11 hours, but he did not come out.
She said Mr Khashoggi was required to surrender his mobile phone, which is standard practice in some diplomatic missions. He told her to call an adviser to Turkish President Recep Tayyip Erdogan if he did not return.
Jamal Khashoggi's fiancée Hatice waited outside the Saudi consulate on Wednesday EPA
"Jamal is not dead. I cannot believe that he has been killed...!" Ms Cengiz wrote on Twitter as the allegations circulated. She said she was waiting for official confirmation.
The head of the Turkish-Arab Media Association, Turan Kislakci, told the New York Times that Turkish police officers providing security for the consulate had checked their security cameras and did not see the journalist leave on foot. But he added that diplomatic cars had been seen moving in and out.
What have the Saudis said?
On Wednesday, Crown Prince Mohammed bin Salman told Bloomberg News that Turkish authorities were welcome to search the building because "we have nothing to hide".
The prince said the Saudis were "very keen to know what happened to him", saying his understanding was that Mr Khashoggi left "after a few minutes or one hour".
The Saudi consulate said Khashoggi left after completing paperwork AFP
When asked if Mr Khashoggi faced charges in Saudi Arabia, the crown prince said his country would need to know where he was first.
Potential crisis
Analysis by the BBC's Mark Lowen, Istanbul
This is a bombshell allegation by Turkey. 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. Ankara's relationship with Riyadh is too important to jeopardise on the basis of unsubstantiated rumour.
That relationship is already strained over several issues, including Turkey's support for Qatar in the blockade by Saudi Arabia; its closeness to the Muslim Brotherhood - blacklisted by Riyadh as a terrorist organisation; and its rapprochement with Saudi Arabia's arch-rival Iran. But if proven, the murder of Jamal Khashoggi would be the most serious diplomatic crisis between the two in living memory.
Turkey would hope for backing from its Nato ally, the US. But Saudi Arabia has arguably become Donald Trump's closest ally in the Middle East - and Washington may be reluctant to weigh in against Riyadh at this stage.
Who is Jamal Khashoggi?
The 59-year-old journalist is one of the most prominent critics of the crown prince, who has unveiled reforms praised by the West while carrying out an apparent crackdown on 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.
A former editor of the al-Watan newspaper and a short-lived Saudi TV news channel, Mr Khashoggi was for years seen as close to the Saudi royal family. He served as an adviser to senior Saudi officials.
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 US, from where he wrote opinion pieces for the Washington Post and continued to appear on Arab and Western TV channels.
"I have left my home, my family and my job, and I am raising my voice," he wrote in September 2017. "To do otherwise would betray those who languish in prison. I can speak when so many cannot."
The Washington Post on Friday blanked out his column in support.
Courtesy: www.bbc.com
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New Delhi, Nov 26: The National Anti-Doping Agency on Tuesday suspended Bajrang Punia for four years for his refusal to provide his sample for dope test on March 10 during selection trials for the national team.
NADA had first suspended the Tokyo Games bronze medallist wrestler on April 23 for the offence following which, the World Governing body UWW had also suspended him.
Bajrang had appealed against the provisional suspension and NADA’s Anti-Disciplinary Doping panel (ADDP) had revoked it on May 31 till NADA issues the notice of charge.
NADA, then on June 23 served the notice to the wrestler.
Bajrang, who joined Congress along with fellow wrestler Vinesh Phogat and was given charge of All India Kisan Congress, had challenged the charge on July 11 in a written submission following which hearings were held on September 20 and October 4.
"The Panel holds that the Athlete is liable for sanctions under Article 10.3.1 and liable for ineligibility for a period of 4 years," the ADDP said in its order.
The suspension means that Bajrang will not be able to return to competitive wrestling and apply for a coaching job abroad, if he aspires to.
"In the present case, since the Athlete had been provisionally suspended, the Panel accordingly holds that the Athlete’s period of his ineligibility for the period of 4 years shall commence from the date on which the notification was sent, i.e., 23.04.2024.
"Needless to say that on account of the lifting of the provisional suspension for the period from 31.05.2024 to 21.06.2024 shall not be credited into the total period of ineligibility of four years."
Bajrang has maintained since the beginning that he was given extremely prejudicial and unfair treatment with respect to doping control because of his involvement in the protest against former WFI President Brij Bhushan Sharan Singh.
Bajrang also maintained that he never refused to give sample but only demanded to know NADA’s response to his email where he sought answer why expired kits were sent to take his samples in December 2023.
NADA also explained the reason for its action, saying that the Chaperone/DCO had duly approached him and informed that he was required to provide a urine sample for dope analysis purposes.
Bajrang in his written submission said that the conduct of NADA in two previous instances had created mistrust in the athlete's mind, especially with NADA failing to acknowledge or even respond to their callous approach towards the doping control process in both such instances, the failure to take responsibility for their action pertaining to their dispersal of duties meant that the athlete was morally bound to take a stance in resort as a senior athlete who holds a voice in the sporting community.
Bajrang also said "it was not an outright refusal per se. The athlete was always willing to provide his sample provided that he first received a response from NADA concerning the use of expired kits."
However NADA said, "the outright refusal by the athlete to provide urine sample for the dope test was intentional and deliberate" and that "Athlete has demonstrated utter disregard towards his duties and responsibilities as per Articles 20.1 & 20.2 of the Anti Doping Rules, 2021."