In Diyala province's Baquba, the US military said three American soldiers were killed in a suicide attack.
It was not immediately clear if it was the same incident in which police reported that a roadside bomb in Baquba, targeting a US foot patrol, killed at least three children, two of them siblings, and wounded seven people.
In what could be the latest in a series of incidents involving the US military and Iraqi civilians, a US convoy was involved in the killing of two Iraqis on Sunday.
"Iraq is still under foreign occupation and Iraqis continue to die in great numbers"
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A statement from the US military and embassy in Baghdad said that initial reports indicated "an incident involving a US military convoy resulted in the death of two Iraqi citizens and wounded four others".
The governor of the southern Shia province of Muthanna had earlier accused US troops of opening fire on civilian cars near Rumaitha, north of the provincial capital Samawa.
Also on Sunday, a parked car bomb targeting a police patrol in Mosul killed three people, including a woman, police said. Four policemen were among the 16 people wounded.
In Tikrit, police said a roadside bomb killed two Iraqi soldiers and wounded another while they were trying to defuse a bomb.
And in the capital, roadside bombs wounded two people in the Ameen district of southeastern Baghdad, and wounded another two in the Kesra neighbourhood of northern Baghdad.
Despite the latest fatalities, the US military said violence in Iraq had fallen sharply over the last few months.
Rear Admiral Gregory Smith, a US military spokesman, said attacks had fallen by 55-per cent since a deployment of an extra 30,000 US troops was completed in June.
Attacks are now at their lowest level since January 2006, according to the US military. It added the drop in attacks was across the board, with Iraqi civilian casualties down 60 per cent.
Aside from the increased number of troops, the reported drop in violence was also attributed to improving Iraqi security forces and the growing use of US-backed local police units organised by mainly Sunni Arab tribal sheikhs.