The top American commander in Iraq says the US probably had a role in civilian casualties in the battle to retake Mosul from Islamic State.
Scores of civilians have died in coalition airstrikes in the west of the city this month as US-backed government forces fight to defeat IS jihadists, according to Iraqi officials.
General Stephen Townsend, head of the anti-IS coalition in Baghdad, said coalition forces were "probably" involved in the deaths of civilians during recent bombings.
But he also cautioned that IS could have played a part.
He said: "My initial assessment is that we probably had a role in these casualties. What I don't know is were they (the civilians) gathered there by the enemy?"
Around 200 civilians are feared to have been killed in a single incident on 17 March in Mosul's al Jadida area.
Investigators are trying to work out whether a coalition airstrike or Islamic State-rigged explosives caused a deadly explosion there.
Some residents said an aerial strike hit an explosive-filled truck and the subsequent blast led to the collapse of buildings packed with families.
Gen Townsend said: "My initial impression is the enemy had a hand in this. And there's also a fair chance that our strike had some role in it. I think it's probably going to play out to be some sort of combination."
The United Nations expressed profound concern over the incident, saying it was "stunned by this terrible loss of life".
The US Central Command said on Saturday a review found a US-led coalition operation, requested by Iraq's government, struck IS fighters and equipment "at the location corresponding to allegations of civilian casualties".