UN officials have expressed concern at the number of civilians killed in air strikes and said more care must be taken in military operations to protect them.
Major Peggy Kageleiry, a US military spokeswoman in northern Iraq, said an Apache attack helicopter had spotted five men planting a roadside bomb near the city of Samarra, 100km north of the Iraqi capital.
"Iraq is still under foreign occupation and Iraqis continue to die in great numbers"
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The helicopter "engaged" the men, who then ran into a nearby house that was also targeted.
Kageleiry said an initial investigation showed five "military age males" and six civilians were killed in the attack.
"They chose to go into a house with civilians to hide. They endangered folks on the ground by doing that.
"We send condolences to the families of those victims and we regret any loss of life," she said.
But police and residents of the village of Djila gave a different account.
They said the group of men attacked by the helicopter were three farmers who had left their homes at 4.30am (01:30GMT) to irrigate their fields.
Two were killed in the initial air attack and the survivor ran back to his home, where other residents then gathered, said Abdul al-Rahman Iyadeh, a relative of the victims.
The second air strike destroyed the house, killing 14 people, he said.
Captain Abdullah al-Isawi, a local police officer, put the death toll at 16 people, made up of seven men, six women and three children.
The US military is already investigating another deadly air attack in which nine children and six women were killed on October 11 during an operation targeting supposed al-Qaeda leaders 80km northwest of Baghdad.
The Iraqi government has also protested against a weekend raid by US forces in the Shia stronghold of Sadr City.
In that incident, US troops backed by helicopters said they killed 49 armed men. Police put the toll at 13 and said all were civilians, including two children.
Critics say US forces often call in air attacks on buildings where fighters are believed to be hiding without taking reasonable care to find out who else might be inside.
The US military insists fighters deliberately hide among civilians.