Turkish police claimed on Saturday that a prominent Saudi Arabian journalist critical of the kingdom's rulers was murdered in its consulate in Istanbul.
A senior Turkish police source told MEE that Khashoggi had been "brutally tortured, killed and cut into pieces".
His disappearance and reported murder in Istanbul "sends a petrifying signal to peaceful dissidents and critics that they are at risk even outside the country, and that the authorities are targeting them one by one wherever they can do so", said Lynn Maalouf, the director of Middle East Research at Amnesty International.
The state-run Saudi Press Agency carried a statement from the Istanbul Consulate that 'strongly denounced these baseless allegations, and expressed his doubt that they came from Turkish officials that are informed of the investigation or are authorised to comment on the issue'.
Fears are growing over missing Washington Post writer Jamal Khashoggi, after Turkish officials said they believe he has been murdered.
The BBC's Istanbul correspondent, Mark Lowen, said it would plunge Turkish-Saudi relations into an unprecedented crisis.
"Also included in these agreements are that part of these armaments will be manufactured in Saudi Arabia, so it will create jobs in America and Saudi Arabia, good trade, good benefits for both countries and also good economic growth". They offered no evidence to support the theory, and Turkey's government has not officially announced any conclusions from the investigation.
Khashoggi, a former newspaper editor in Saudi Arabia and adviser to its former head of intelligence, left the country a year ago saying he feared retribution for his growing criticism of Saudi policy in the Yemen war and its crackdown on dissent.
The Saudi source said that a security team including Saudi investigators had arrived in Istanbul on Saturday to take part in the investigation into Khashoggi's disappearance.
Khashoggi's disappearance is likely to further deepen divisions between Turkey and Saudi Arabia. Turkish authorities have said that Khashoggi never left the consulate.
"I'm not sure. We are investigating this through the foreign ministry to see exactly what happened at that time", he added.
'Jamal was - or, as we hope, is - a committed, courageous journalist.
"We are ready to welcome the Turkish government to go and search our premises", he said, which is Saudi sovereign territory. 'We have nothing to hide'.
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.
He reached the consulate on Tuesday to secure documentation for a forthcoming marriage, according to his fiancée, who waited outside.
In an article published by Al-Jazeera this week, journalist and analyst Bill Law described Khashoggi as "a brilliant journalist with a fiercely independent mind but with sufficient pragmatism to know just how close to the red lines he could go".