The Israeli army conceded Monday for the first time that one of its soldiers had likely shot Palestinian-American reporter Shireen Abu Akleh after having mistaken her for a militant.

"There is a high possibility that Ms Abu Akleh was accidentally hit by IDF (Israel Defence Forces) gunfire that was fired toward suspects identified as armed Palestinian gunmen," said the army's final investigation report into her May 11 death.

The acknowledgement comes after months in which the army had insisted it was impossible to determine the source of the deadly shot that killed the celebrated Al Jazeera journalist in the occupied West Bank, saying it could have been militant fire.

"Our conclusion is that it's not possible to determine unequivocally which gunfire killed her, but there's a higher probability that she was hit by an errant shot of an IDF soldier who did not identify her as a journalist," a senior Israeli military officer said.

Abu Akleh was wearing a bulletproof vest marked "Press" and a helmet when she was shot in the head during an Israeli army operation.

The Abu Akleh family said that Israel had "refused to take responsibility for the murder" of the journalist, in a press release issued in the wake of the  army's report.

"We remain deeply hurt, frustrated and disappointed," the family said, calling for a "credible" US investigation.

The Palestinian Authority accused Israel of intentionally killing the reporter in the Jenin refugee camp, in the northern West Bank, whereas Israel has insisted that even if a soldier fired the fatal shot it was not deliberate.

Al-Jazeera said it denounced the findings of the Israeli investigation and demanded a probe by an "independent international body".

"Al Jazeera condemns the Israeli occupation forces' reluctance to explicitly admit their crime and attempts to evade the prosecution of the perpetrators," it said in a statement.

- 'Call for accountability' -

On Monday, the senior army officer told reporters that the soldiers were under heavy fire and aimed to hit Abu Akleh because they had mistaken her for a Palestinian militant.

"When they fired in her direction they didn't know she was a journalist, it was a mistake, they thought they were firing at terrorists shooting at them," the officer said.

"He's sorry about it and I'm sorry about it too," the officer said of the soldier who shot in the direction of Abu Akleh.

"He didn't do it on purpose, it's totally clear," he added.

But the New York-based Committee to Protect Journalists was critical of the army's report.

Its "admission of guilt is late and incomplete. They provided no name for Shireen Abu Akleh's killer and no other information than his or her own testimony that the killing was a mistake," said Sherif Mansour, CPJ's Middle East and North Africa programme coordinator.

Israeli rights group B'Tselem, a campaigner against Israeli settlement expansion, condemned the army's report as a "whitewash". The killing was "no mistake, it's policy", it said.

A United Nations investigation concluded in June that there was "no evidence of activity by armed Palestinians close by" when Abu Akleh was shot.

The United States on July 4 said she was likely shot by Israeli fire but that there was no evidence her killing was intentional and that the bullet was too damaged for a conclusive finding.

After the release of the army report on Monday, State Department spokesman Ned Price said: "We welcome Israel’s review of this tragic incident, and again underscore the importance of accountability in this case, such as policies and procedures to prevent similar incidents from occurring in the future."

The US statement in July outraged Abu Akleh's family and Palestinian leaders who accused Washington of failing to seek accountability from Israel over the killing of the journalist, who also held US citizenship.

"We are continuing to call for accountability and for justice for Shireen," Lina Abu Akleh, the journalist's niece, said in Washington after meeting US Secretary of State Antony Blinken.

In May, Israel's military advocate had said there was no suspicion of criminal activity since the event took place in an active combat zone.

The military advocate said Monday that the circumstances of the incident "do not raise the suspicion of a crime having been committed which would justify the opening of a criminal investigation".