Their white Mercedes was blown to smithereens late on Saturday in the restive town, 180 km north of Baghdad, a US military commander said on Sunday.
"It appeared to be an attempt to place a roadside bomb. Those attempting to place it detonated it, killing themselves," said Lieutenant Colonel Steve Russell, commander of the 1-22 Battalion of the US 4th Infantry Division that patrols the town.
"There were three people in the vehicle, two were killed and one was injured and is now under police custody in a Tikrit hospital," he told AFP.
Russell said he believed a car of the same description was used in previous resistance attacks against occupation forces in the Tikrit area, including one on 16 December in which three US soldiers were wounded.