The "indirect fire attack" was on Camp Bucca near the southern port city of Basra, said the statement, adding that no US servicemembers were killed or wounded.

Of the some 19,000 Iraqis held in US-run facilities, 13,000 are held in Camp Bucca.

A suicide truck bomb struck an Iraqi army base on Saturday southwest of Baghdad, killing 12 soldiers and wounding 30, army and medical officials said.

Iraqi Army Lieutenant Mohammed Fatlawi said the attack took place at a base near the town of Iskandiriyah, 60km south of Baghdad.

Doctor Ali Shammari from the town's general hospital also confirmed the attack.

Earlier three people died in separate attacks in Baghdad on Saturday, while the US military said its troops killed six militants in a series of raids across the country.

A car bomb detonated next to a National Police patrol killing a policemen and a bystander and wounding 12 others in Baghdad's northeast Shia neighbourhood of al-Shaab, a defence official said.

A medic at Imam Ali hospital in nearby Sadr City confirmed the attack and said the bodies of the two victims were received by the facility.

Eight of the wounded were also admitted to the hospital, including six policemen, he added.

Another policeman was killed in a separate clash with armed men in the same neighbourhood.

In Zafaraniyah in southern Baghdad, three people were wounded by a roadside bomb aimed at a police patrol, a medic at Ibn Nafis hospital said.

Late Friday, gunmen ambushed a car and killed five members of a family on the main road near Kanan, located in the restive Diyala province, northeast of Baghdad, police Lieutenant Ahmed Ali said.

The dead included a woman.

Diyala is the second most dangerous province in Iraq after Baghdad and insurgents have stepped up attacks there after a massive security crackdown in the capital since February.

The US military, meanwhile, said its forces had carried out a series of raids on Saturday in which five militants were killed.

In a raid southeast of Fallujah, the former rebel town in the western province of Anbar, US troops targeted a weapons distributor for the al-Qaeda in Iraq network.

"As they approached the area, five men in the front yard reached for weapons. Responding appropriately to the hostile threat, coalition forces engaged the armed men, including the suspected distributor killing them," a military statement said.

An Iraqi boy was wounded in the firefight, the military said.

The military announced the death of one more militant in a similar raid but did not specify when the raid was conducted.

More than a dozen suspected militants were also arrested during the raids, the military added.