In other violence, five members of an Awakening Council were killed when gunmen attacked two separate checkpoints near Tikrit on Thursday, 80 miles north of Baghdad. Nine others were wounded.
A suicide bomber also attacked an Awakening Council gathering in the village of Zab outside Kirkuk, 180 miles north of Baghdad. Three people were killed and seven others wounded in that attack.
Awakening Councils are made up of mostly Sunni fighters who have accepted US backing to switch allegiances and fight al-Qaida in Iraq.
The violence comes amid a sharp increase in attacks resulting in the deaths of US soldiers. Twelve Americans have been killed in the past four days, bringing the overall US military death toll since the start of the war near 4,000.
Three soldiers died Wednesday in a rocket attack on Combat Outpost Adder near Nasiriyah, about 200 miles southeast of Baghdad. A day earlier a soldier died when a roadside bomb hit his patrol near Diwaniyah, 80 miles south of Baghdad. Eight soldiers were killed in two bomb attacks on Monday, the heaviest single day of US casualties since September.
Three of those soldiers died in a roadside bombing in Diyala, a violent province where al-Qaida in Iraq has been active. The five others were killed when approached by a suicide bomber while on foot patrol in central Baghdad.
The Islamic State of Iraq, a Sunni militant group, issued a statement Wednesday claiming responsibility for the soldiers' deaths.
At least 3,987 members of the US military have died since the beginning of the Iraq war in March 2003, according to an AP count. The figure includes eight military civilians.