The US military has admitted that three Iraqi civilians killed in an explosion on Friday died because of an artillery training exercise that went wrong.
An artillery round fired from a US military base near Hibhib (about 20km north of Baquba) struck a building in the nearby town, a statement said.
Two Iraqis were killed instantly, while a third died later from her wounds.
This comes amid investigations of a number of incidents in which civilians were killed by US troops.
Last week, Iraqi Prime Minister Nuri Maliki expressed concern about the increase in the number of deadly incidents described as mistakes by the US military, saying there was "a limit to acceptable excuses".
Most attention has been focused on an incident in the town of Haditha where US marines are alleged to have killed up to 24 Iraqi civilians in November 2005.
Troops fired the 155mm shell from the base near Baquba, the US military statement said.
"A short time later Iraqi police reported an explosion at a building in the town [Hibhib] that killed two Iraqi civilians, injured four others and damaged six houses," it said.
It added that an injured woman was taken to a military medical facility but later died.
US forces went to the site of the explosion to provide medical assistance, the statement said.