A US military spokeswoman said 11 US troops were among the wounded in what was the first major attack in Samarra since its was wrested from Iraqi fighters in a deadly offensive by US and Iraqi troops at the start of October.
"A pair of vehicle-concealed IEDs [improvised explosive devices] detonated near the city centre in Samarra" on Wednesday, the spokeswoman said.
She the bombs killed one child and injured 11 US troops and an Iraqi civilian.
Dr Husain Allah al-Din said four children were killed and 20 people wounded in the blast in Samarra, a battle-scarred city north of Baghdad.
The casualties were evacuated to Samarra's general hospital.
Police commander Salah Husain said it was a car-bomb attack, adding that one of the US army vehicles in the convoy had been damaged.
Area sealed off
Residents said the US army had sealed off the area and announced a curfew in the city.
The US-Iraqi offensive on Samarra in early October, which the US military says killed more than 150 people, including 20 civilians, marked the first major push to take cities from Iraqi fighters before January national elections.
US and Iraqi troops have also been
US and Iraqi troops have also been encircling the city of Falluja, west of Baghdad.
Also on Wednesday, a car bomb exploded on the road to Baghdad's international airport, killing the driver.
Hours later, another car packed with explosives detonated beside a convoy of US tanks on the western edge of Haifa Street, a known trouble spot in Baghdad, causing no casualties.