Iraqi police say gunmen wearing military uniforms opened fire on two checkpoints in the western town of Haditha early Monday, killing at least 27.
The victims include two top police commanders who were kidnapped from their homes and executed. At least one of the gunmen was killed.
Haditha is under a curfew while police investigate.
It is unclear who was behind Monday's pre-dawn attack, but a police spokesman tells the French news Agency, AFP, that al-Qaida is responsible.
Haditha became an al-Qaida stronghold after Saddam Hussein was overthrown in 2003.
Some information for this report was provided by AP, AFP and Reuters.