Michael Lawrence, Reuters managing editor for Europe, Middle East and Africa, said on Sunday: "Reuters calls on the US government to conduct a full and objective investigation into the death of Waleed Khaled."
An independent inquiry commissioned by Reuters concluded that the soldiers' shooting of Waleed Khaled on August 28 last year appeared "unlawful".
But the Pentagon has failed to respond to requests to review the local commander's ruling, which said the firing of shots at the car was "appropriate".
In April, Reuters gave the US defence department the report, which found the soldiers' own evidence did not support the commander's conclusion.
The report also criticised the military for "losing" vital video footage of the incident shot by the Reuters cameraman who was Khaled's passenger. He was wounded and then arrested by troops.
"The defence department has ignored the independent report which concluded that US soldiers breached their rules of engagement and the shooting of Waleed was prima facie unlawful," Lawrence said.
More than 100 journalists have been killed in Iraq since 2003.