A Pentagon investigation has found that more than 100 civilians were killed after the US dropped a bomb on a building in Mosul, Iraq, in March.
The probe found that the American bomb triggered secondary explosions from devices clandestinely planted there by Islamic State (IS) fighters.
The secondary blasts caused the concrete building to collapse, according to the US military.
It is likely to be the largest single incident of civilian deaths since the US air campaign against IS began in 2014.
The lead investigator is Air Force Brigadier General Matthew Isler.
He said 101 civilians in the building were killed, and another four died in a nearby building. He added that 36 civilians remain unaccounted for.
The deaths represent about a quarter of all civilian deaths since the US air campaign began.