Three civilians were killed and three soldiers wounded in a bomb blast targeting a US military convoy in the capital's Sadr City Shia bastion on Friday, a US military spokesman said.
"An improvised explosive device at 0400 GMT killed three civilians and wounded three of our soldiers," said Captain Brian.
The bomb was hidden in the mud off the curb of an open-air market in the Habibiya district of Sadr City, O'Malley told AFP.
He said the attack appeared to be targeting the convoy.
US soldiers killed two insurgents on Friday in the second straight day of fighting around the Iraqi village of Bohrouz, north-east of Baghdad, the US military said.
"This morning, coalition forces received sporadic fire from two insurgents firing rocket-propelled grenades," said Master Sergeant Cynthia Weasner of the 1st Infantry Division.
"The two insurgents were killed".