“To date, based on information available, CJTF-OIR [Combined Joint Task Force] assesses that, it is more likely than not, at least 484 civilians have been unintentionally killed by coalition strikes since the start of Operation Inherent Resolve,” read a report by Operation Inherent Resolve released on Friday.

According to the report, a total of 21,035 airstrikes, including 44,330 separate engagements, were carried out against ISIS between August 2014 and April 2017.

The report also showed that the total number of dead civilians increased by more than a third as last month’s report acknowledged 352 civilian deaths.

 The increase was mostly the result of an airstrike carried out on March 17 in the Iraqi city of Mosul, during which “101 civilians sheltered in the bottom floors of the structure, and four civilians in a neighboring structure were killed.”

Meanwhile, independent monitors say that coalition strikes have led to significantly more civilian casualties.

The United States and its allies formed the coalition in 2014 with a purported aim of fighting ISIS in neighboring Iraq, but they later expanded it to include territories in eastern and northern Syria.

The US-led coalition has repeatedly been accused of targeting and killing civilians. It has also been largely incapable of fulfilling its declared aim of destroying ISIS.