The US administration has granted immunity to Saudi Crown Prince Mohammed bin Salman, possibly derailing a civil lawsuit filed against the kingdom’s day-to-day ruler over the 2018 murder of commentator Jamal Khashoggi.

The administration based the decision on Prince Mohammed having recently been appointed as Saudi Arabia’s prime minister. In a court document filed on Thursday, the US Department of Justice said Washington had “expressed grave concerns” over Khashoggi’s “horrific killing” and also shared intelligence officers’ review of Riyadh’s role in the matter and had imposed sanctions. But it argued that “the doctrine of head of state immunity is well-established in customary international law”.

Khashoggi’s murder at the hands of Saudi security agents in the kingdom’s consulate in Istanbul has haunted relations between Saudi Arabia and the US under president Joe Biden, who came to office vowing to turn Prince Mohammed and Saudi Arabia into a “pariah”. The CIA had determined the prince sanctioned a “capture or kill” mission against Khashoggi, a former insider turned columnist who wrote for the Washington Post.