In this Oct. 2, 2017 photo, family members bury their relative in a graveyard in Mosul after his body was exhumed hours earlier. Under Iraqi law, Mosul residents must recover the bodies of their relatives killed during the final battle to oust Islamic State from the city in order to receive a death certificate from the government. (AP Photo/Bram Janssen)
In this Oct. 2, 2017 photo, family members bury their relative in a graveyard in Mosul after his body was exhumed hours earlier. Under Iraqi law, Mosul residents must recover the bodies of their relatives killed during the final battle to oust Islamic State from the city in order to receive a death certificate from the government. (AP Photo/Bram Janssen) Credit: Bram Janssen

Mosul, Iraq — Between 9,000 and 11,000 people were killed in the nine-month battle to liberate the Iraqi city of Mosul from the Islamic State group, a civilian casualty rate nearly 10 times higher than has been previously reported, an Associated Press investigation has found.

The deaths are acknowledged neither by the U.S.-led coalition, the Iraqi government nor IS’s self-styled caliphate.

Iraqi or coalition forces are responsible for at least 3,200 civilian deaths from airstrikes, artillery fire or mortar rounds between October 2016 and the fall of IS in July 2017, according to the AP investigation, which cross-referenced morgue lists and multiple databases from non-governmental organizations. Most of those victims are simply described as “crushed” in health ministry reports.

The coalition, which did not send anyone into Mosul to investigate, acknowledges responsibility for only 326 of the deaths.

“It was the biggest assault on a city in a couple of generations, all told. And thousands died,” said Chris Woods, head of Airwars, an independent organization that documents air and artillery strikes in Iraq and Syria and shared its database with AP.

“Understanding how those civilians died, and obviously ISIS played a big part in that as well, could help save a lot of lives the next time something like this has to happen. And the disinterest in any sort of investigation is very disheartening,” Woods said, using an alternative acronym for IS.

In addition to the Airwars database, the AP analyzed information from Amnesty International, Iraq Body Count and a United Nations report. The AP also obtained a list of 9,606 names of people killed during the operation from Mosul’s morgue. Hundreds of dead are believed to be buried in the rubble.

Of the nearly 10,000 deaths the AP found, around a third of the casualties died in bombardment by the U.S.-led coalition or Iraqi forces. Another third were killed in Islamic State militants’ final frenzy of violence. And it could not be determined which side was responsible for the deaths of the remainder.

Iraqi Prime Minister Haidar al-Abadi told the AP that 1,260 civilians were killed in the fighting. The U.S.-led coalition has not offered an overall figure. The coalition relies on drone footage, video from cameras mounted on weapons systems and pilot observations for investigations.