The US State Department has said that that independent investigators could not reach a definitive conclusion regarding the origin of the bullet that killed Palestinian-American journalist Shireen Abu Akleh after conducting detailed forensic analysis.

"Ballistic experts determined the bullet was badly damaged, which prevented a clear conclusion," State Department spokesman Ned Price said in a statement after what he called "extremely detailed forensic analysis" of the bullet reluctantly handed over by the Palestinian Authority.

Shireen Abu Akleh, who held US citizenship and was one of the best-known Palestinian journalists, was fatally shot as she covered an Israeli army operation in Jenin in the occupied West Bank despite wearing a vest that said "Press."

Her death provoked a furor, with the Palestinian Authority alleging she was shot intentionally in what amounted to a war crime - charges angrily denied by Israel, a close US ally which President Joe Biden is visiting in two weeks.

The US Security Coordinator (USSC), which directs security assistance to the Palestinian Authority in coordination with Israel, said that both sides granted full access to their own probes over the past several weeks.

"By summarizing both investigations, the USSC concluded that gunfire from IDF positions was likely responsible for the death of Shireen Abu Akleh," the State Department said, referring to the Israeli Defense Forces.

"The USSC found no reason to believe that this was intentional but rather the result of tragic circumstances during an IDF-led military operation against factions of Palestinian Islamic Jihad," it said.

Family 'incredulous'

Ms Abu Akleh's family said in a statement it was "incredulous" that the examination could not determine whose gun fired the bullet that killed her.

"We will continue to advocate for justice for Shireen, and to hold the Israeli military and government accountable, no matter the attempts to obfuscate the reality of what happened on May 11," it said.

Senior Palestinian Authority official Hussein Al Sheikh condemned efforts to "conceal the truth" over Ms Abu Akleh's death, writing on Twitter that there should not be "shy references in pointing the finger of accusation to Israel".

The Palestinian Authority's attorney general, Akram Al-Khatib, told AFP on Saturday that the bullet was handed over to US forensic experts - and not Israel - on the condition that there would be no modifications and that it would be returned.

But an Israeli army statement said that Israeli experts examined the bullet at a laboratory in the Jewish state - while the State Department said the process involved "independent, third-party examiners".

Israel had publicly accused the Palestinians of stonewalling on an investigation by not handing over the bullet - while the Palestinians in turn feared Israel would whitewash any probe it leads.