An ongoing review of air and artillery strikes found another 51 civilians were killed by the US-led coalition in Iraq and Syria, pushing the total toll to at least 786.

In a statement Thursday, the coalition said that in September it completed an analysis of 127 reports of civilian deaths dating back to when international operations to defeat the Islamic State group got underway in late 2014.

Most reports were deemed "non-credible" or duplicative, but 16 had merit, the coalition found.

"To date, based on information available, (the coalition) assesses at least 786 civilians have been unintentionally killed by coalition strikes since the start" of the campaign, the statement read.

Among the many reports the coalition examined last month was a March 20 strike on an IS building in Tabqa, Syria, that left 10 civilians dead.

And a June 25 strike in Mayadin in eastern Syria killed 12 civilians when an IS-held building was hit.

"Although all feasible precautions were taken and the decision to strike complied with the law of armed conflict, unintended civilian casualties unfortunately occurred," the statement read.

Observers say the US-led coalition has been taking greater risks with civilian lives since President Donald Trump took office and gave the military greater leeway in how it conducts strikes, but officials insist the rules of engagement are unchanged.

The coalition conducted 27,566 strikes between September 2014 and September 2017.

During this time, 1,266 reports of civilian casualties were made, but the coalition found only 194 of these to be credible.

The coalition also noted that more than 95 percent of the territory once held by IS in Iraq and Syria has been liberated.

Aside from probing civilian death reports that came in from coalition pilots and through social media and other channels including IS claims, military investigators also are scrutinizing a backlog of hundreds of allegations reported by the website Airwars.org.

The London-based collective of journalists and researchers has always had civilian death tolls that are wildly divergent from those acknowledged by the coalition, putting the number killed in US-led strikes at 5,637 as of Thursday.