The State Department also said the United States could not make a "definitive conclusion" on the origin of the bullet that killed her on May 11, which was handed over by the Palestinian Authority.
"Ballistic experts determined the bullet was badly damaged, which prevented a clear conclusion," State Department spokesman Ned Price said after what he called "extremely detailed forensic analysis" with outside examiners.
Abu Akleh's death provoked a furore, with the Palestinian Authority alleging a war crime, prompting angry denials 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.
"We will remain engaged with Israel and the PA on next steps and urge accountability. We again offer our deepest condolences to the Abu Akleh family," said the rare July 4 statement.
The iconic Al Jazeera journalist, who held US citizenship, was killed as she was covering an Israeli army operation in the Jenin camp in the north of the occupied West Bank.
The Palestinian probe said that an Israeli soldier shot her dead.
Further inflaming tensions, baton-wielding Israeli police descended on mourners during her funeral and grabbed Palestinian flags, with the pallbearers struggling not to drop her casket.
Several media outlets have also pointed to Israel in the killing, with a CNN report saying she appeared to have been targeted by Israeli forces.
A New York Times investigation found that the bullet was fired from near the location of an Israeli military convoy, likely by a soldier from an elite unit and that there were no armed Palestinians in the area.
But the newspaper also did not ascertain whether the shooter targeted her personally or could see that she and her colleagues wore vests that identified them as journalists.
Israeli leaders have insisted that it would not target a journalist. Israel initially said she could have been killed by Palestinian gunfire but later backtracked and promised an investigation.
Dozens of US lawmakers had urged the United States to take the lead in conducting its own investigation, saying that there was a need for an impartial finding.
Secretary of State Antony Blinken spoke to Abu Akleh's family and has criticized the Israeli police's use of force at her funeral, while insisting since May that not all facts were known about how she was killed.