Citing civilian and military officials briefed on the case, the New York Times reported on its website last night that the US justice department was reviewing the findings of the FBI, which was continuing to investigate the incident in Baghdad on September 16.
No evidence supported assertions by Blackwater employees that they were fired upon by Iraqi civilians, the Times reported.
It said the FBI had concluded that three of the deaths may have been justified under rules that allow lethal force in response to an imminent threat.
Investigators concluded that as many as five of Blackwater guards opened fire during the shootings, the newspaper said.
One guard has become the focus of the investigation, the Times reported, because that guard was responsible for several deaths.
A government official familiar with the investigation told the Associated Press that no conclusions had been reached about any of the fatalities. A US state department official said he was not aware that the department had been informed of any findings. Both requested anonymity because the investigation was continuing.
A Blackwater spokeswoman, Anne Tyrrell, said the company "supports the stringent accountability of the industry".
She said: "If it is determined that one person was complicit in the wrongdoing, we would support accountability in that. The key people in this have not spoken with investigators."
Blackwater has said its convoy was attacked before its personnel opened fire, but an Iraqi government investigation concluded that the shootings were unprovoked.
State department officials have said it has offered limited immunity to private security contractors involved in shootings in Iraq. They disagreed with law enforcement officials that such actions could jeopardise prosecutions in the September 16 incident.