All six victims were members of the same family from the village of al-Jisr, according to Falljuah Hospital’s Dr Ayman al-Ani on Tuesday.
Al-Ani identified the dead as Ali, Saadi and Salim al-Jumaili.
Relatives in al-Jisr said US occupation forces encircled the village about 1:30am (2130 GMT) and began using machine guns before the helicopter missile attack.
One correspondent at the scene said the attack was apparently aimed at two other houses, which only suffered damage, but were not destroyed.
US military officials in Baghdad and Central Command said they had no immediate information on any operation
No spokesman was prepared to discuss whether those members of the al-Jumaili family who survived would be compensated for the homicides and destruction of property.
Local residents celebrate after a
resistance attack hits US troops
A military spokesman in Fallujah was also unavailable for comment when contacted by Aljazeera.net.
The operation came just hours after 250 people demonstrated in Fallujah, 50km west of Baghdad, demanding US-led occupation force should leave Iraq to Iraqis.
A minority of the protesters even carried portraits of former president Saddam Hussein, and called for his return to power.
But there was no indication whether there was any link between the two events.
Fallujah and the surrounding area have been the scene of frequent clashes and attacks on US troops.