Pentagon: 'No one will ever know' civilian toll of anti-IS fight

The US military said "no one will ever know" how many Iraqis and Syrians its troops and allies killed in the four-year fight against the Islamic State group.

The Pentagon said on Tuesday that despite "best efforts" to count civilian casualties in air strikes against IS targets, there was "no possible way" and that anyone who knows is "lying".

The admission comes after rights group Amnesty International accused the US and its allies of killing hundreds of civilians during its campaign to retake the Syrian city of Raqqa from IS extremists. 

"As far as how do we know how many civilians were killed, I am just being honest, no one will ever know," US Army Col Thomas Veale, spokesman for the US led coalition fighting IS in Iraq and Syria, said in a briefing at the Pentagon by video link from Baghdad. "Anyone who claims they will know is lying, and there's no possible way."

Veale described civilian deaths as "extremely unfortunate" and a "terrible, awful part of this war" against IS.

Amnesty on Tuesday said the US-led coalition's 2017 assault on Raqqa killed hundreds of civilians and could amount to war crimes.

Researchers for the rights group interviewed more than 100 residents and visited sites of 42 air, artillery and mortar strikes in the city in a two-week period in February. 

It said that in the four cases detailed in its report, air strikes using powerful munitions had hit buildings full of civilians who had been staying there for long periods.

One family told Amnesty it lost 39 members to coalition strikes.

In its monthly casualty reports, the coalition has acknowledged responsibility for 32 civilian deaths in Raqqa between June and October 2017, while saying it is still investigating open cases. Meanwhile indepedent monitoring group Airwars says it has evidence of 1,400 fatalities.

Veale objected to the report's prima facie argument that the US had violated international law by endangering the lives of civilians.

"They are literally judging us as guilty until proven innocent. That's a bold rhetorical move by an organisation that fails to check the public record or consult the accused."

Amnesty investigators called on the coalition to release strike data and details on the decision-making process behind target selection. They said the coalition rebuffed requests for information.