Three suicide bombers targeted checkpoints in Iraq's northern city of Mosul late on Thursday, killing three policemen, police sources said.
The violence is part of a recent wave of attacks that is stoking fears of a return to the intercommunal strife following the withdrawal of U.S. troops in December 2011.
Police sources said two of the bombers drove cars into checkpoints in the city of Mosul.
Prime Minister Nuri al-Maliki, a Shi'ite Muslim, is facing mass protests by disenchanted Sunnis and is at loggerheads with ethnic Kurds who run their northern region autonomously from Baghdad.
The prospect of provincial elections is hardening the divisions as political leaders appeal to their constituencies with hostile and uncompromising rhetoric.
The conflict in neighbouring Syria, where mainly Sunni rebels are fighting to overthrow a leader backed by Shi'ite Iran, is also whipping up sectarian tensions in Iraq and across the wider region.