The coalition said in a statement that it had completed a review in March of 49 reports of potential civilian casualties from air and artillery strikes, of which all but three were deemed not credible.

These three incidents occurred in Iraq and Syria last year.

On May 25, near Al-Mayadin in Syria's eastern province of Deir Ezzor, 15 people were killed during an air strike on an IS "media center and headquarters."

"The investigation assessed that although all feasible precautions were taken and the decision to strike complied with the law of armed conflict, unintended civilian casualties unfortunately occurred," officials said in a statement.

An April 27, 2017 strike on an IS headquarters in the Syrian city of Raqa saw 11 civilians killed, and a May 16 strike saw two people killed.

Investigators were still looking at another 476 reports from the campaign.

The coalition conducted a total of 29,254 strikes between August 2014 and the end of March 2018 in Iraq and Syria.

Monitoring group Airwars says the number of civilian deaths acknowledged by the US-led coalition is well below the true toll of the bombing campaign, estimating that at least 6,259 civilians have been killed.

The US-led operations to fight IS in Iraq and Syria have largely wound down, with the jihadists ousted from more than 98 percent of the territory they once held.

The coalition's toll of non-fighters killed dates from 2014.