"There have been no reports of coalition forces firing on anyone or any vehicle in the area," Brigadier General Mark Kimmitt, the coalition's deputy director of operations, told a press conference in Baghdad on Sunday.
He said that US troops found three people - a man, woman and child - dead in a vehicle on Saturday morning on a road in Tikrit and that it appeared they were victims of gunshot wounds.
US soldiers were told at the scene that a fourth occupant was wounded in the incident and taken to a hospital in Tikrit, the hometown of captured dictator Saddam Hussein, Kimmitt said.
"We are hoping the fourth occupant will provide some information about what happened," he said.
On Saturday Tikrit's police chief told AFP that four Iraqis, including a woman and a child, were killed when a US convoy opened fire on their car in the town.
"The car, a grey Chevrolet Caprice, was hit by 27 shots and skidded, resulting in the death of four people, including a woman and a nine year-old child," said Colonel Ussama Adham Abdel Ghaffer.
The 4th Infantry Division's head
denied his troops were involved
A fifth occupant who survived the incident with chest injuries also said the vehicle had received fire from a US convoy.
US Lieutenant Colonel Steve Russell, head of the 4th Infantry Division battalion which patrols the Tikrit area, said at the time he was aware of a shooting incident involving a civilian car, but stressed that his men were not involved.