The coalition said in a statement that it had completed a review in February of 84 reports of potential civilian casualties from air and artillery strikes, of which all but six were deemed not credible.

These six incidents occurred in Syria between May 2017 and January 2018.

In one instance, five civilians were killed near Albu Kamal during a coalition strike against an Islamic State leader.

"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.

Investigators were still looking at another 522 reports from the campaign.

The coalition conducted a total of 29,225 strikes between August 2014 and the end of February 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 6,238 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.