US troops killed three fighters who fired on their convoy after trying to ram it on Friday in Mosul, 390km north of Baghdad, the American military said.
The soldiers then opened fire on two cars that approached the patrol and appeared to be hostile, killing five civilians, the military said. The incident is under investigation.
Three civilians, believed to be municipal workers, were killed and four people were wounded in a Baghdad bomb blast on Saturday, hospital officials said.
The explosion, at 7.30am (0330 GMT), in Baghdad's southern district of Dura, was caused by a roadside bomb and might have caught the workers as they cleaned the street, medics said.
An Interior Ministry official confirmed there had been a blast, but put the toll at one dead and three wounded.
In a separate attack a US soldier was killed and four others were wounded when a car bomb exploded on Friday near their patrol near Baiji, about 180km north of Baghdad, the US military said in a statement.
At least 1238 US military and Pentagon personnel have been killed in action in Iraq since the start of the 2003 invasion, according to Pentagon figures.
An explosion rocked central Baghdad on Saturday, sending a large plume of smoke rising into the sky.
The cause of the blast at 1.25pm (0925 GMT) was not clear. The US military had no immediate information.