The U.S. is asking Saudi Arabia behind closed doors to hold a former top official implicated in the murder of Washington Post columnist Jamal Khashoggi to account, according to a report published Monday.

Riyadh has thus far staunchly resisted U.S. pressure to take action against Saud al-Qahtani over Khashoggi's Oct. 2 slaying in the Saudi consulate in Istanbul, The Wall Street Journal reported, citing anonymous Saudi and American officials.

Al-Qahtani previously served as the de facto right-hand man to Crown Prince Mohammed bin Salman, a post he has since been formally removed from even as he has continued to serve as an informal adviser to Saudi Arabia's royal court.

“We don’t see that Saud al-Qahtani is very constrained in his activities,” an anonymous senior State Department official told the newspaper.

Al-Qahtani was one of 17 Saudis sanctioned by the U.S. in December over Khashoggi's killing. Turkey is also seeking his extradition.

Saudi officials confirmed to the Journal that he remains an informal advisor to bin Salman, the Kingdom's de facto ruler, even after he was fired by Saudi King Salman.

Pressure has continued on the U.S. administration to hold bin Salman personally responsible for Khashoggi's killing, but it has so far resisted.

Last Friday, President Donald Trump ignored a congressional deadline to publicly determine whether sanctions are warranted against bin Salman.