Residence of Saudi Arabia's Consul General
© Reuters/Huseyin Aldemir (L) - Reuters/Picture Archive (R)Residence of Saudi Arabia's Consul General Mohammad al-Otaibi
The UN's high commissioner for human rights has called to drop diplomatic immunity of Saudi officials to allow for a transparent investigation over the disappearance of dissident Saudi journalist Jamal Khashoggi.

Michelle Bachelet made the plea on Tuesday as US Secretary of State Mike Pompeo touched down in the Saudi capital Riyadh to talk to King Salman about Khashoggi's disappearance.

"In view of the seriousness of the situation surrounding the disappearance of Mr Khashoggi, I believe the inviolability or immunity of the relevant premises and officials bestowed by treaties such as the 1963 Vienna Convention on Consular Relations should be waived immediately," Bachelet said in a statement.

Khashoggi entered the Saudi consulate building in Istanbul on October 2 in order to collect documents that would allow him to get married. He hasn't been seen since.

Pompeo's visit coincides with reports in US media on Monday night that the Saudi government was preparing a report that will admit that Khashoggi died as a result of a botched interrogation.

Living in self-imposed exile between the US and Turkey since last year, Khashoggi worked as a columnist for the Washington Post.

Critical of the Saudi regime's crackdown of dissenting voices and its bombing of Yemen, his writings were an uncomfortable counterpoint to Saudi Crown Prince Mohammed bin Salman's desire to portray the country as one that was modernizing.

Turkish police fear Khashoggi was killed by a Saudi hit squad who touched down in and left Istanbul the day of the journalist's visit to the consulate - a claim Riyadh has repeatedly denied over the last two weeks.

Bachelet urged both the Saudis and investigating Turkish authorities to "reveal everything they know about the disappearance and possible extrajudicial killing."

"Given there seems to be clear evidence that Mr Khashoggi entered the consulate and has never been seen since, the onus is on the Saudi authorities to reveal what happened to him from that point onwards," she added.

Turkish forensic investigators searched the consulate building overnight, almost two weeks after Khashoggi was first reported missing.

Questioning the length of time between the disappearance and the search, Bachelet said it was a "very long time for the probable scene of a crime not to have been subjected to a full forensic investigation."

Police will now search the Saudi consul's residence in Istanbul, located near the consulate, where it is believed that Khashoggi may have been taken in a van at some point during the operation.