At least 27 members of Iraq's security forces are reported to have been killed in a wave of attacks that targeted checkpoints in the city of Haditha, in the western Anbar province.
Police sources told Al Jazeera on Monday that the attacks specifically targeted police personnel across several checkpoints. The dead included two police colonels.
Lieutenant-Colonel Owaid Khalaf told the AFP news agency that dozens of armed men carried out the attacks, which began late on Sunday.
Prime Minister Nouri al-Maliki has reportedly sacked the top security official in Anbar province, Lieutenant General Abdul Aziz Al Obaidi.
Al Jazeera's Jane Arraf, reporting from Baghdad, said Haditha remained under curfew as authorities searched for the assailants.
"This was obviously a very well-planned attack," she said,
"It began when gunmen, dozens of them according to police sources, commandeered and stole SWAT vehicles. The SWAT teams are part of the counterterrorism forces. They drove around the city, dressed as SWAT members, in black-and-blue uniforms. As they were stopped at a checkpoint, they opened fire."
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The assailants also entered the homes of a colonel and a captain in the interior ministry security force, kidnapping them and shooting them, Mohammed Fathi, a spokesman for Anbar's governor, told the Associated Press news agency.
The two commanders were later found shot dead in the street not far from their homes, Haditha police said.
Fathi said the attackers had false arrest warrants for 15 police officers in Haditha.
Major Tareq Sayeh Hardan, a police spokesman in Haditha, blamed al-Qaeda for the attacks, saying that literature belonging to the group had been found in one of the attackers' vehicles.
The attacks in Haditha are the first major instance of violence in the city since a suicide bomber blew himself up inside a bank, killing nine people, including three police officers, and wounding eight others on March 2011.
Haditha is in the mostly Sunni Arab province of Anbar. It was one of several towns along the Euphrates valley that became al-Qaeda strongholds after the 2003 US-led invasion that removed Saddam Hussein from power.
Tribal leaders and thousands of Sunni fighters eventually turned against al-Qaeda, forcing the group's fighters out of the town.
Tension has also risen between Anbar and the federal government recently, following an arrest campaign against former members of Saddam's banned Baath party.