Protestors hold placards as they stage a protest outside the Saudi Arabian Embassy in Paris (AFP)
Jamal Khashoggi was strangled to death the moment he entered the Saudi consulate in Istanbul, the citys chief prosecutor said on Wednesday, adding that it was a premeditated murder.
The journalists body was dismembered and the whereabouts of his remains are unknown, Irfan Fidan said in a statement.
"In accordance with plans made in advance, the victim, Jamal Khashoggi, was strangled to death immediately after entering the Consulate General of Saudi Arabia in Istanbul on 2 October 2018 for marriage formalities," he said.
"The victim's body was dismembered and destroyed following his death by suffocation – again, in line with advance plans," it added.
The statement follows a series of meetings between Fidan and the Saudi chief prosecutor Saud al-Mujeb.
"Despite our well-intentioned efforts to reveal the truth, no concrete results have come out of those meetings."
Saudi Arabia has now invited Fidan to the kingdom, where 18 suspects have apparently been apprehended, to continue his investigation.
Turkish President Recep Tayyip Erdogan said on Tuesday that the Saudis were protecting the person responsible for Khashoggi's murder, adding that Turkey would not abandon its investigation.
"A game to save somebody lies beneath this," Erdogan told reporters following a speech in parliament. "We won't leave Khashoggi's murder behind."
So far, the kingdom has placed the blame for Khashoggi's murder on two of Crown Prince Mohammed bin Salman's closest allies, deputy intelligence chief Ahmed al-Assiri and top aide Saoud al-Qahtani, who was once dubbed "Saudi Arabia's Steve Bannon". Both men have been fired.
Many observers, however, believe the 33-year-old heir to the Saudi throne is behind the murder, despite his claims to the contrary.
The news comes as a group of five Republican senators asked US President Donald Trump to suspend upcoming nuclear talks with Saudi Arabia.
"The ongoing revelations about the murder of Saudi journalist Jamal Khashoggi, as well as certain Saudi actions related to Yemen and Lebanon, have raised further serious concerns about the transparency, accountability, and judgment of current decision-makers in Saudi Arabia," the group, led by former presidential candidate Marco Rubio, wrote in a letter to the president.
"We therefore request that you suspend any related negotiations for a US-Saudi civil nuclear agreement for the foreseeable future."
The group said they would use an obscure provision in the Atomic Energy Act to block US-Saudi nuclear agreements if the talks were not called off.