The casualties occurred on Monday in Haditha, according to Basim Izz al-Din, a doctor in the local hospital.
The town lies 220km northwest of Baghdad in a mainly Sunni province which includes the cities of Falluja and Ramadi.
Fighting in al-Anbar has already claimed the lives of several US soldiers in the past few days.
The 1st Marine Expeditionary Force released a statement on Monday saying three soldiers attached to the marines died in two incidents on Sunday "while conducting security and stability operations" in the area.
Earlier, the military said two marines had been killed in action in Anbar on Friday.
Elsewhere on Monday, US troops battled fighters along Baghdad's busy Haifa Street, sending passersby scurrying for cover and forcing stores to close, witnesses said.
The fighting broke out after armed men appeared on the street saying they were hunting for Iraqis collaborating with US forces.
An oil pipeline near Samarra
has been set ablaze
Witnesses said they shot and killed a man they said was working for the Americans on Tahrir Square.
The fighters were also seen on Mathaf Square, just three blocks from the heavily fortified Green Zone that houses Iraq's interim government and the US embassy.
The US military had no immediate comment, but witnesses said US troops supported by armoured vehicles fought pitched battles with the men.
Haifa Street, a thoroughfare running through central Baghdad, has been the scene of frequent clashes between US troops and fighters opposed to the US-sponsored interim government in Iraq.
Also on Monday, an official in the Diyala police directorate, Brigadier Jalil Karim, was seriously injured when assailants opened fire at him in the al-Tahrir neighbourhood in central Baquba city, Aljazeera learned.
Karim's driver and two civilians were also injured in the attack.
Aljazeera also learned that an oil pipeline linking the Baiji refinery to Baghdad was ablaze near Samarra city, north of the capital.
Elsewhere, a series of explosions rocked the US military headquarters in al-Mualimin neighbourhood in central Samarra city. Columns of smoke could be seen rising from the site.