The deceased were members of a wedding party who were reportedly shot dead by US troops when traditional gunfire at the wedding was mistaken for hostile fire.
The US army has launched an investigation into the deaths in the town of Samarra, north of the capital, after doctors reported that they had been killed as they rode through the streets firing in the air to celebrate the wedding.
“Gunfire during celebrations can be interpreted as hostile fire and prompt return of fire," an occupation radio warned.
"It blocks the reconstruction process and the flying in of humanitarian aid to certain regions."
New weapons controls announced by occupation ground forces commander Lieutenant General David McKiernan last week included a ban on celebratory fire, although he acknowledged it would be difficult to enforce as the practice was "part of the culture".
In a bid to secure the country, US forces have imposed a 14 June deadline for handguns and automatic rifles to be submitted to occupation troops.