Two policemen and a soldier were gunned down on Sunday in separate incidents in the city of Mosul, the capital of Nineveh province, a provincial police source said, Xinhua reported.
The three were killed by unidentified armed men while manning checkpoints in central and eastern Mosul, the source told Xinhua on condition of anonymity.
Iraqi security forces blocked several neighborhoods and main streets in the city following the attacks, searching for the attackers, the source said.
Mosul, some 400 km north of Baghdad, remains one of Iraq's most volatile cities despite the dramatic drop of violence in Iraq over the past two years.