By Nick Childs
BBC Pentagon Correspondent
The US military is also investigating claims of unlawful killing in Falluja
The US military has charged an army officer with the killing of an injured Iraqi in Baghdad in August.
Two soldiers have already been charged with murder over the same incident.
The move comes as the Americans began investigating the fatal shooting by a US marine of an injured insurgent in the city of Falluja on Saturday.
The officer, 2nd Lieutenant Erick Anderson, has been charged with premeditated murder and conspiracy to commit premeditated murder.
He was charged with the killing of an injured Iraqi in August in the volatile Sadr City slum area of the Iraqi capital, Baghdad.
A similar incident was captured in Falluja on camera by an embedded American television journalist working for US network NBC over the weekend.
Pentagon officials insist they are taking that matter very seriously, while also arguing that it would be wrong to rush to judgement on the case before all the facts have been collected.
Clearly these are hugely sensitive cases, but some Pentagon officials argue that it is a measure of how seriously they take such matters generally that there have been a number of probes into alleged unlawful killings in Iraq.
Several murder charges have already been brought against US personnel, of which those against the army officer are only the latest.