In a statement, the military said the five were killed during a raid early today targeting an Al-Qaeda cell in Mosul.
It said U.S. forces expressed their sympathies after the men turned out to be Kurdish police. Kurdish officials put the death toll at eight.
In other violence, Iraqi authorities earlier said gunmen posing as Iraqi Army soldiers killed at least 11 civilians and kidnapped another 13 in the town of Imam, south of Baghdad.
The violence came as U.S. and Iraqi reinforcements were continuing to move into Baghdad in new security operations intended to quell fighting.
(Reuters, AFP, AP)