“Disappearance and alleged murder of Jamal Khashoggi requires immediate and independent international investigation,” David Kaye tweeted on Sunday.
Jamal Khashoggi missing on Tuesday after entering the Saudi consulate in Istanbul.
Kaye said such probe was necessary to “protect any investigation against claims of politicization or bad faith.”
The investigation would also “demonstrate international abhorrence of crimes against journalists,” he added.
“Honestly, if all the resolutions in UN about safety of journos mean anything, they must mean, here, investigation and accountability (prosecution, reparations, diplomatic consequences, etc),” the official said.
Also on Sunday, Yasin Aktay, an advisor to Turkish President Recep Tayyip Erdogan, said he believed that Khashoggi had been killed inside the consulate.
Erdogan, however, said he was still hopeful about his fate.
"It is also extremely saddening that this incident took place in our country. I knew Mr. Jamal for a long time; therefore my expectations are still positive," the Turkish head of state told reporters. "There is a security investigation on the issue; there is an intelligence investigation on the issue.
Specifically all the entries and exits in and out of Istanbul's airports are under investigation," Erdogan added.
A day earlier, Saudi Crown Prince Mohammed bin Salman had denied speculation that Riyadh had taken Khashoggi in, stressing that Turkey could search the consulate for him. “If he’s in Saudi Arabia, I would know that,” bin Salman had alleged.
Khashoggi, a prominent commentator on Saudi affairs who writes for The Washington Post
’s Global Opinions section, has lived in self-imposed exile in the United States since September 2017. He left Saudi Arabia that year over fears of the Riyadh regime’s crackdown on critical voices.
He had reached the consulate to secure documentation for a forthcoming marriage, according to his fiancée, who waited outside.