ISTANBUL (Reuters) - Turkey's ruling party said on Monday Jamal Khashoggi was the victim of a "monstrously planned" murder, dismissing Riyadh's assertion he died in a fight, as Western incredulity deepened over varying Saudi accounts of the journalist's disappearance.
Khashoggi, a Washington Post columnist and critic of the powerful Saudi crown prince, disappeared three weeks ago after he entered the Saudi consulate in Istanbul to obtain documents for an upcoming marriage.
Riyadh's reaction since - it initially denied knowledge of his fate before saying he was killed in a fight in the consulate - has left several Western governments deeply sceptical and strained ties with the world's largest oil exporter.
Ruling AK Party spokesman Omer Celik said efforts had been made to cover up the killing, referring to surveillance footage aired by CNN showing a man dressed as Khashoggi walking around Istanbul after he vanished in an apparent attempt at deception.
"We are facing a situation that has been monstrously planned and later tried to be covered up. It is a complicated murder," he told reporters.
"We are being careful so nobody tries to cover the issue up. The truth will come out. Those responsible will be punished, something like this will not cross anybody's mind anymore."
Khashoggi went missing on Oct. 2 when he entered the kingdom's consulate in Istanbul. After weeks of denying knowledge of his fate, Saudi officials said the prominent journalist was killed in a "fistfight".
On Sunday Saudi Arabia's Foreign Minister, Adel al-Jubeir, said that Khashoggi had died in a rogue operation. But some of his comments appeared to contradict previous statements from Riyadh, marking yet another shift in the official story.
Several countries, including Germany, Britain, France and Turkey, have pressed Riyadh to provide all the facts, and Chancellor Angela Merkel said Berlin would not export arms to Saudi Arabia while uncertainty over Khashoggi's fate persisted.
"One cannot help but wonder how there could have been a 'fistfight' between 15 young expert fighters ... and a 60-year-old Khashoggi, alone and defenceless," Yasin Aktay, an adviser to Turkish President Tayyip Erdogan and a friend of Khashoggi's, wrote in the pro-government Yeni Safak newspaper.
"The more one thinks about it, the more it feels like our intelligence is being mocked," he wrote.
Erdogan has said he will release information about Turkey's investigation in a speech on Tuesday.
Turkish officials suspect Khashoggi was killed inside the consulate by Saudi agents and his body cut up. Turkish sources say authorities have an audio recording purportedly documenting the murder of the 59-year-old.
A car belonging to the Saudi consulate in Istanbul was found in the Sultangazi district of the city, broadcaster NTV and other local media said on Monday, adding that police would search the vehicle.
For Saudi Arabia's allies, the question will be whether they believe that Crown Prince Mohammed bin Salman, who has painted himself as a reformer, has any culpability. King Salman, 82, has handed the day-to-day running of Saudi Arabia to him.
In some critical areas, Jubeir's explanation appeared to depart from previous official statements.
He said the Saudis did not know how Khashoggi had died. That contradicted the public prosecutor's statement a day earlier that Khashoggi died after a fistfight with people who met him inside the consulate. It also contradicted two Saudi officials' comments to Reuters that it was a chokehold that killed him.
A member of the team dressed in Khashoggi's clothes to make it appear as if he had left the consulate, a Saudi official has said. Support for that strand of the account appeared to come from footage aired by CNN showing a man dressed as Khashoggi walking around Istanbul. CNN described the images as law enforcement surveillance footage.
Some top U.S. lawmakers turned their ire on the crown prince and said they believed he ordered the killing. "Do I think he did it? Yes, I think he did it," Republican Senator Bob Corker, the influential chairman of the Senate Foreign Relations Committee, said in an interview with CNN.
Over the course of the crisis, Trump's comments have varied from appearing to downplay Riyadh's role in the incident, to warning of potential economic sanctions. He has repeatedly highlighted the kingdom's importance as an ally.
(Editing by William Maclean)