WASHINGTON, United States: A new survey conducted by an army mental health advisory team showed that almost one in ten US combat troops deployed in Iraq have mistreated a civilian.

The report also found that less than half of the soldiers and marines surveyed would report a fellow serviceman for killing or injuring an innocent Iraqi.

"Soldiers with high levels of anger, who had experienced high levels of combat or who screened positive for mental health symptoms were nearly twice as likely to mistreat noncombatants," Major General Gale Pollock, the acting army surgeon general, told reporters at a press conference.

The most common mistreatment reported by soldiers and marines was that of insulting non-combatants in their presence, the report said.

The survey showed that 55 per cent of US army soldiers, and only 40 per cent of marines, would report a fellow serviceman for killing or injuring an innocent non-combatant.

The survey, which shows increasing rates of mental health problems for troops on extended or multiple deployments in Iraq, was the first to include questions on ethics and ethical training.

As such, the report stresses the findings cannot be compared "with any other group of military personnel".