JERUSALEM >> Israel’s Defense Minister Benny Gantz said Monday the U.S. Department of Justice has launched an investigation into the fatal shooting of Palestinian-American Al Jazeera journalist Shireen Abu Akleh, condemning the probe as a “grave mistake” and vowing not to cooperate.

A Justice Department spokesman did not immediately respond to a request for comment and there were no details about when an investigation might have begun and what it would entail, nor what the ramifications of it might be. But a probe by the U.S. into Israeli actions would be a rare step.

A probe would pose a direct challenge to Israel’s claims that it properly holds its soldiers to account for its actions in the Palestinian territories and would shake the strategic U.S.-Israel alliance at a time when Israel is bracing for the formation of its most right-wing government ever and as progressive Democrats in the U.S. have called for a harder line against Israel.

Gantz made the statement on Twitter, saying Israel has made it clear to the U.S. “that we won’t cooperate with any external investigation.”

“We will not allow interference in Israel’s internal affairs,” he added. Gantz, who is set to leave his post following elections earlier this month, served as defense minister when Abu Akleh was killed.

A Palestinian who covered Israeli operations in the Palestinian territories for years, Abu Akleh was also a U.S. citizen and her family had demanded a full U.S. investigation into her death.

Abu Akleh’s brother, Tony Abu Akleh, told Al Jazeera the family was optimistic, saying it’s “very important to hold those responsible accountable and prevent similar crimes.”

“We hope this will be a turning point in the investigation into Shireen’s death,” he said.

Palestinian officials, Abu Akleh’s family and Al Jazeera accuse Israel of intentionally targeting and killing the 51-year-old journalist, who was wearing a helmet and a protective vest marked with the word “press” when she was shot last May in the occupied West Bank.

She had covered the West Bank for Al Jazeera for two decades and was a well-known face across the Arab world. Her death reverberated across the region.

Palestinian Foreign Ministry officials did not immediately respond to requests for comment late Monday. A spokeswoman for outgoing Israeli Prime Minister Yair Lapid declined to comment, and former Prime Minister Benjamin Netanyahu, who is expected to return to lead the country in the coming weeks, also had no immediate comment.

A series of investigations by international media outlets, including by The Associated Press, found that Israeli troops most likely fired the fatal bullet. The United States concluded that an Israeli soldier likely killed her by mistake, but it did not explain how it reached that conclusion.

Following its own investigation, Israel acknowledged that Israeli fire probably killed Abu Akleh, but vigorously denied allegations that a soldier intentionally targeted her.

It is not unusual for the FBI or other U.S. investigators to mount probes into non-natural deaths or injuries of American citizens abroad, particularly if they are government employees.

However, such separate investigations are not the rule and it is rare, if not unprecedented, for them to occur in a U.S.-allied country like Israel that is recognized in Washington as having a credible and independent judicial system.

Critics have long accused the military of doing a poor job of investigating wrongdoing by its troops and seldom holding forces accountable. Following their own investigation into the death, Israeli authorities decided not to launch a criminal investigation.

Abu Akleh was covering an Israeli military raid in the Jenin refugee camp in the West Bank. The area has been the focus of months of nightly Israeli arrest operations that were launched following a spate of Palestinian attacks against Israelis in the spring that killed 19 people.

More than 130 Palestinians in east Jerusalem and the West Bank have been killed this year, making 2022 the deadliest year since 2006. Israel says most of those killed have been militants, but local youth protesting the raids as well as people not involved in the fighting have also been killed.

The Israeli raids have prompted a series of Palestinian shooting attacks that have killed at least four Israelis in recent weeks.

The probe comes weeks after Netanyahu secured what looked like a clear path to returning to the leadership after national elections. He is currently holding talks with his ultra-Orthodox and ultranationalist allies over forming a government and is expected to cobble together Israel’s most right-wing government ever.

The government, which is expected to see extremist lawmakers appointed to key ministries, is likely to prompt concern among Israel’s global allies, including the U.S.