Iraqi authorities arrested at least 13 alleged Al-Qaeda fighters on Tuesday in connection with a shooting spree that left 27 policemen dead, including two officers killed execution-style.

The men, apparently led by an ex-officer in the late Saddam Hussein's elite Republican Guards, were arrested in Salaheddin and Anbar provinces, north and west of Baghdad, defence ministry spokesman Major General Mohammed al-Askari told AFP.

Another man blew himself up when cornered by security forces, and three were killed in clashes, Askari said.

"We intensified our operations on instruction from the operations commands of Salaheddin and Anbar, and we arrested 13 members of Al-Qaeda," he said.

"Three others were killed during the operation, and a fourth one blew himself up."

The interior ministry earlier said that police in Salaheddin arrested four suspects, and a fifth blew himself up. It was unclear if the four men the interior ministry spoke of were among the 13 Askari said were detained.

On Monday morning, suspected Al-Qaeda gunmen, some wearing army uniforms, raged through the western city of Haditha, in Anbar province, in a pre-dawn shooting spree that killed 27 policemen.

The assault, launched at about 2:00 am (2300 GMT on Sunday), saw insurgents dressed in military uniforms simultaneously attacking two checkpoints in the east and west of Haditha before storming other security posts and raiding the homes of two officers.

Authorities sacked Lieutenant General Abdulaziz Mohammed Jassim, head of Anbar province's security command centre, in the aftermath of the attack.

Haditha was one of several towns along the Euphrates valley that became Al-Qaeda strongholds after the 2003 US-led invasion that ousted Saddam Hussein.

However, in 2006, local Sunni tribes sided with the US military and unrest dwindled in Anbar as rebel fighters were ejected from the region.

Violence across the country is down from its peaks in 2006 and 2007, but attacks remain common. A total of 150 Iraqis were killed in February, according to official figures.