Four Iraqi policemen were killed and eight others were wounded by US fire on Sunday in what was called a "mistake", said police from the north-eastern city of Khanaqin.
According to Sirwan Shukr, a local official, four US helicopters struck a police centre "by mistake".
"Perhaps the US forces suspected that the centre belonged to terrorist groups," said Shukr, who added that the US military had not provided an explanation yet.
The victims are all policemen belonging to the Kurdish Peshmerga forces.
In another incident, at least 97 suspected terrorists were captured in the early hours on Sunday.
According to Khoshid Mahmoud, a senior policemen in Kirkuk, 250 km north of Baghdad, the city's police troops rounded-up the suspects during a "massive operation" targeting militants, especially those who fled from Diyala province.
Unlicensed weaponry was also seized during the said raids.