Prominent journalist and Washington Post contributor Jamal Khashoggi was reportedly killed at the Saudi consulate in Istanbul in what the paper's sources are calling "a preplanned murder".
"If Khashoggi was indeed murdered inside a diplomatic facility, it is an act of terror that echoes Russian and Chinese tactics of extraterritorial, extrajudicial attacks on dissidents, meant to intimidate any who would speak out against the Saudi government, no matter where they may be, and giving the lie to official narratives of "reform" in Saudi Arabia", said Summer Lopez, of PEN America.
A close friend of Khashoggi told DPA news agency that police had informed him about their conclusions, saying his body was cut into pieces. Both spoke on the condition of anonymity to discuss the ongoing investigation.
Khashoggi disappeared after entering the diplomatic mission on Tuesday.
In his newspaper columns, Khashoggi has been critical of some policies of Saudi Crown Prince Mohammed bin Salman and Riyadh's intervention in the war in Yemen.
"The official strongly denounced these baseless allegations", the agency wrote, adding that a team of Saudi investigators were in Turkey working with local authorities.
Another unnamed government official told AFP that: "Based on their initial findings, the police believe that the journalist was killed by a team especially sent to Istanbul and who left the same day".
Yasin Aktay, who advises the Turkish leader in his ruling Justice and Development (AK) Party, made the comments in a brief interview with Reuters on Sunday, adding that Turkish authorities further believed that a group of 15 Saudi nationals were "most certainly involved" in the matter.
Khashoggi has lived in self-imposed exile in the USA since 2017 fearing arrest for his critical views of Saudi Crown Prince Mohammed bin Salman.
On Friday, bin Salman confirmed to the press that Khashoggi's visit was indeed a quick in and out, saying his understanding was that the journalist left the consulate within an hour of first entering.
Khashoggi went to the consulate to receive an official document for his marriage.
Turkey would hope for backing from its North Atlantic Treaty Organisation ally, the US.
"The premises are sovereign territory, but we will allow them to enter and search and do whatever they want to do".
Saudi Consul-General Mohammad al-Otaibi told Reuters on Saturday that the consulate's own security cameras showed only a live stream and did not record footage, so they could not provide evidence of Khashoggi's movements. "He writes out of a sense of love for his country and deep faith in human dignity and freedom".
Turkish media said prosecutors were now looking closely at the case, although this may be a widening of an inquiry begun on Tuesday. Relations were already strained after Turkey sent troops to the Gulf state of Qatar previous year in a show of support after its Gulf neighbors, including Saudi Arabia, imposed an embargo on Doha.
PEN America, which promotes free expression around the world, also called on Saudi authorities to produce Khashoggi immediately if they "wish to counter these claims".