"Shortly after the incident, coalition forces leaders met with a sheikh representing the citizens of the local area," a US military statement said.
"The incident is under investigation. We offer our condolences to the families of those who were killed in this incident, and we mourn the loss of innocent civilian life."
The statement gave no further details.
Iraqi police said that US helicopters had fired on a checkpoint manned by a neighbourhood police patrol and several woman were among the victims.
Saturday's strike was the deadliest case of "mistaken identity" acknowledged by US forces in recent months.
In November, a leader of one of the so-called awakening councils, Sunni tribesmen allied with American forces in fighting to oust al-Qaeda from their towns, said that US soldiers had killed dozens of his fighters during a 12-hour battle north of Baghdad.
Mansour Abid Salim, the leader of the Taji Awakening Council, accused US troops of mistaking his men for fighters.
The military admitted killing 25 men, but said they were "insurgents" operating "in the target area" where al-Qaeda was believed to be hiding.
Critics say US forces often call in air raids on targets, including buildings where opposition fighters are believed to be hiding, without taking reasonable care to find out who might be inside.
The US military says that armed groups often deliberately use civilians as shields against attacking US forces.