Gunmen disguised as police raided checkpoints and homes in western Iraq on Monday, killing at least 27 members of the security forces.
The brazen attacks in the town of Haditha in Anbar raise concern that Iraq's branch of al Qaeda may regain a foothold in the province after the withdrawal of United States troops in December last year, Reuters reports.
Anbar was almost entirely under control of al Qaeda during the height of Iraq's insurgency from 2005-07, when the militants were defeated by local tribesmen and American forces.
A government spokesperson said the attackers arrived at checkpoints with fake arrest warrants, confiscated the mobile phones of the police guards and executed them.
A curfew has been imposed on Haditha and its exits sealed off.
Iraq is due to host a summit of the Arab League later in March and its leaders have been at pains to say that security is under control.
Al Qaeda and other Sunni militant groups oppose the Shi'ite-led government in Baghdad and say they will continue to fight despite the withdrawal of US forces.