Palestinian authorities have handed the bullet that killed journalist Shireen Abu Akleh to a team of US investigators, Palestinian Authority attorney Gen Akram Khatib announced on Saturday.

Forensic investigators are expected to confirm that the bullet was fired from an Israeli army rifle, the central claim of a Palestinian Authority investigation into the killing.

Last month, the UN Human Rights Office said the Israeli army had fired the fatal shot near the Jenin refugee camp in the West Bank.

The Palestinian-American journalist, who had covered the Israel-Palestine conflict for 25 years, was struck in the head by a bullet on May 11 during a gun battle between Israeli soldiers and Palestinian militants. She had been reporting on an Israeli army raid with colleagues early that morning. The team of Al Jazeera journalists wore blue body armour and helmets emblazoned with the word “Press”.

An official Palestinian investigation into the May 11 killing concluded that the bullet was fired by an Israeli army Ruger Mini-14 rifle.

“Examination of the fired projectile revealed that it is a calibre of 5.56 millimetres and that it bears a mark and general and individual characteristics that match the general marks of the Mini-14 Ruger weapon, which is a semi-automatic sniper weapon,” Gen Khatib said of the initial investigation.

The Palestinian Authority was assured that no modifications would be made to the bullet and that it would be returned as soon as the assessment was complete, Gen Khatib told AFP.

The authority agreed to hand over the bullet to the US, but not to Israel, the official Wafa Palestinian news agency reported.

US Secretary of State Antony Blinken promised last month to pursue accountability over the killing of Abu Akleh wherever the facts might lead.

"We are looking for an independent, credible investigation. When that investigation happens, we will follow the facts, wherever they lead. It's as straightforward as that," said Blinken.

Investigations by the UN and journalists have found that the shot that killed Abu Akleh was fired by Israeli forces.

"We find that the shots that killed Abu Akleh came from Israeli security forces," UN Human Rights Office spokeswoman Ravina Shamdasani told reporters in Geneva.

"It is deeply disturbing that Israeli authorities have not conducted a criminal investigation."

The UN rights office inspected photo, video and audio material, visited the scene, consulted experts, reviewed official communications and interviewed witnesses.

The probe examined submissions from the Israeli army and the Palestinian attorney general.

However, the Israeli army branded the UN's findings unfounded, insisting it was "not possible" to determine how Abu Akleh was killed.

"The IDF [Israel Defence Force] investigation clearly concludes that Ms Abu Akleh was not intentionally shot by an IDF soldier and that it is not possible to determine whether she was killed by a Palestinian gunman shooting indiscriminately ... or inadvertently by an IDF soldier," the military said.