"During the operation, gunfire killed a 12-year-old boy located inside the target building," a US military statement said.
"Ground forces detained the suspect and immediately transported the boy to a nearby medical facility where he subsequently died of his wounds," it said.
"Coalition forces are reviewing the incident to determine the exact circumstances surrounding the boy's death," it added. "It is unfortunate that terrorists deliberately surround themselves with women and children."
The detained militant was not identified, except as allegedly "one of the main foreign terrorist facilitators in Iraq."
In a separate operation in the Julaiba district of Baghdad, a US air strike "killed one terrorist and wounded another after coalition forces observed the individuals loading a vehicle with illegal weapons and explosives."
The suspects had been under surveillance and were suspected of planting roadside booby traps. When the were spotted loading their car, US troops called in air support and the vehicle was destroyed.

Copyright AFP (Agence France-Presse), 2006