WASHINGTON (AP) — It raised eyebrows six weeks ago when Saudi Arabia's aged king, Salman, named his son, Crown Prince Mohammed bin Salman, as prime minister. The kingdom's laws designate the king as prime minister. King Salman had to declare a temporary exception to loan out the title, and at the same time made clear he retains key duties.

But that move reaped dividends Thursday, when the Biden administration declared that Prince Mohammed's standing as prime minister shielded him from a U.S. lawsuit over what the U.S. intelligence community says was his role in Saudi officials' 2018 killing of a U.S.-based journalist. A judge will now decide whether Prince Mohammed has immunity.

National Security Council spokesman John Kirby insisted Friday that the administration's declaration of immunity for Saudi Arabia's crown prince was purely a "legal determination" that "has absolutely nothing to do with the merits of the case itself."

Many experts in international law agreed with the administration — but only because of the king's late September title boost for the crown prince, ahead of a scheduled U.S. decision.

"It would have been just as remarkable for the United States to deny MBS's head-of-state immunity after his appointment as Prime Minister as it would have been for the United States to recognize MBS's head-of-state immunity before his appointment," William S. Dodge, a professor at the University of California-Davis School of Law, wrote, using the prince's initials.

State Department spokesman Vedant Patel gave examples Friday of past instances of the U.S. recognizing immunity for heads of government or state — Robert Mugabe of Zimbabwe and Narendra Modi of India, both in allegations of rights abuses.

The lawsuit was filed in federal court in Washington by the fiancée of slain journalist Jamal Khashoggi and by a D.C.-based rights group he founded. It accuses the crown prince and about 20 aides, officers and others of plotting and carrying out Khashoggi's slaying at the Saudi consulate in Istanbul.

The killing, condemned by Biden on the campaign trial in 2019 as "flat-out murder" that must have consequences for Saudi rulers, is at the core of a rift between strategic partners, the United States and Saudi Arabia.

Before and immediately after taking office, Biden vowed to take a stand on Saudi Arabia's crown prince, as part of a presidency that would be based on rights and values. But Biden has since offered a fist bump and other conciliatory gestures in hopes — disappointed so far — of persuading the crown prince to pump more oil for world markets.

Biden's administration argues that Saudi Arabia is too important to the global economy and to regional security to allow the United States to walk away from the decades-old partnership.

But rights advocates, some senior Democratic lawmakers, and Khashoggi's newspaper, The Washington Post, on Friday condemned the administration's move.

"Jamal died again today," Khashoggi's fiancee, Hatice Cengiz, tweeted.

Fred Ryan, publisher of the Post, called it a "cynical, calculated effort" to manipulate the law and shield Prince Mohammed. Khashoggi wrote columns for the Post that in his last months criticized the crown prince's rights abuses.

"By going along with this scheme, President Biden is turning his back on fundamental principles of press freedom and equality," Ryan wrote.

Cengiz and Khashoggi's rights group, Democracy for the Arab World Now, or DAWN, had argued that the crown prince's late September title change was no more than a maneuver to escape U.S. courts, without legal standing or any change in authority or duties.

Saudi Arabia has not commented publicly on the administration's decision. Spokespeople with the Saudi Embassy and Ministry of Foreign Affairs did not immediately respond to an email seeking comment Friday.

Saudi Arabia blames what it says were "rogue" officials for Khashoggi's killing. It says the prince played no part.

Saudi Arabia is an absolute monarchy, as opposed to a constitutional one like the United Kingdom, where a prime minister rather than king or queen governs.

"Pretty pathetic," Sarah Leah Whitson, head of Khashoggi's rights group, said Friday of the title change.

"If anything, it just demonstrated how afraid Mohammed bin Salman was and has been of our lawsuit and actual accountability and actual discovery of his crimes," Whitson said.

The Biden administration appeared to dismiss her group's argument that Prince Mohammed's recent title change ran counter to Saudi Arabia's governing law and should be disregarded.

King Salman has continued making appointments and presiding over meetings of his council since the title change.

But Prince Mohammed for years has been a key decision-maker and actor in the kingdom, including representing the king abroad.

Some Western news outlets had presented the temporary transfer of the prime minister title as King Salman — who is in his late 80s — devolving responsibility to Prince Mohammed, who is 37.

A federal judge had given the U.S. until Thursday to offer an opinion, or not, on the claim by the crown prince that his standing shields him from U.S. courts.

Rights advocates had hoped up to the moment of filing that the administration would stay silent, offering no opinion on Prince Mohammed's immunity either way.

Sovereign immunity, a concept rooted in international law, holds that states and their officials are protected from some legal proceedings in other foreign states' courts.

Prior criminal and civil cases brought against foreign governments and leaders in which the U.S. has not intervened have generally involved countries with which the U.S. has no diplomatic relations or does not recognize their heads of state or government as legitimate.

Cases brought against Iran and North Korea seeking damages for deaths or injuries to American citizens are two prominent examples of instances where the executive branch has not weighed in with an opinion about sovereign immunity.

By contrast, the United States has full diplomatic relations with Saudi Arabia. The State Department stressed Thursday that honoring the principle for other governments' leaders helps ensure that courts in other countries don't seek to haul U.S. presidents before them to answer to lawsuits there.

Kirby, the National Security Council spokesman, said the U.S. decision had "absolutely nothing" to do with "tense" U.S.-Saudi relations over Saudi-led oil production cuts, and other matters.

Biden has been "very, very vocal" about the "brutal, barbaric murder of Khashoggi," Kirby said.

But some of Biden's fellow Democrats in Congress expressed disappointment at the administration's move.

"Is the Administration casting aside its confidence in its own intelligence community's judgment?" Sen. Tim Kaine, a Virginia Democrat, said in a statement. "If the friends and family of Khashoggi are denied a path to accountability in the American court system, where in the world can they go?"

Whitson, the official for Khashoggi's rights group, said the lawsuit would continue against the others named in the lawsuit.

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Associated Press writer Aamer Madhani contributed to this report.