The U.S. Justice Department recently informed the Israeli Justice Ministry that the FBI has opened an investigation into the death of Palestinian American journalist Shireen Abu Akleh, who was killed in May while covering an Israeli military raid in the occupied West Bank city of Jenin, Israeli officials said Monday.

Why it matters: Such an investigation is highly unusual. Israeli Defense Minister Benny Gantz called the FBI decision "a grave mistake" and said Israel will refuse to cooperate.

• The investigation could lead to a U.S. request to investigate the soldiers who were involved in the operation — a request Israel would almost certainly reject.
• The investigation could also lead to tensions between the Biden administration and the Israeli government.

Driving the news: The FBI decision to open an investigation into the case was first reported on Israel’s Channel 14 on Monday.

• Five sources briefed on the issue, including four Israeli officials, confirmed to Axios that DOJ notified the Israeli Justice Ministry about the decision. The sources requested anonymity as they were not authorized to publicly speak on the issue.

What they're saying: Gantz said later Monday that "the U.S. Justice Department decision to investigate the tragic death of Shireen Abu Akleh is a grave mistake."

• "The IDF conducted an independent and professional investigation. I have made it clear to the U.S. government that we won’t cooperate with any external investigation and won’t allow any interference in Israel’s internal affairs,” he added.

White House National Security Council spokesperson referred Axios to the DOJ.

• “Our thoughts remain with the Abu Akleh family as they grieve this tremendous loss. Not only was Shireen an American citizen, she was a fearless reporter whose journalism and pursuit of truth earned her the respect of audiences around the world," the NSC spokesperson added.
• The DOJ did not reply to a request for comment.

Between the lines: The administration has faced pressure by dozens of congressional Democrats and Abu Akleh's family to do more to ensure accountability. More than 20 Democratic senators signed a letter calling for an independent FBI investigation.

• U.S. Sen Chris Van Hollen (D-Md.) said in a statement that "this is an overdue but necessary and important step in the pursuit of justice and accountability in the shooting death of American citizen and journalist, Shireen Abu Akleh."

Flashback: Abu Akleh, an Al Jazeera correspondent, was wearing a bulletproof vest marked "press" when she was killed.

• The Palestinian Authority and her family accused the Israeli military of intentionally targeting her.

The IDF concluded in September she was most likely killed in "unintentional fire" from an Israeli soldier who did not realize she was a journalist. The findings were a shift from the IDF's initial position that it was not possible to know who shot Abu Akleh.

• The Biden administration said in early July that Abu Akleh was likely killed by unintentional Israeli fire, but a ballistics test of the bullet fragment removed from her body was "inconclusive."
• Citing witnesses, as well as visual and audio evidence, independent investigations by several news organizations, including the Washington Post, AP and the New York Times, found that it was likely that an Israeli soldier fired the fatal shot.
• A probe conducted by the UN human rights body came to a similar conclusion.

Editor's note: This story has been updated with additional details throughout.