Wilburn Russell, father of a US soldier charged with slaying five fellow service members, has accused the authorities of 'breaking' his son under stress.

The 73-year-old father said that army officials at Camp Liberty in Iraq forced his son, John M. Russell, to undergo distressing mental ordeals without his prior knowledge of the planned tests and that they "broke him with intent".

He expressed regret about his son's deed, saying, "We're sorry for the families, too. It shouldn't have happened."

Wilburn blames and criticizes the US military for its disconcerting manner in conducting experiments, noting that John had, in recent emails to his family before the shooting incident, dubbed the last number of days "the worst in his life".

"My life is over. To hell with it, I'm going to get even with 'em," Russell quoted his son as saying in one of the last emails sent to him.

The shooting, in which five American troops were killed and three others wounded, took place after the 44-year-old soldier was admitted to the health facilities in the US base in Baghdad for the common Post Traumatic Stress Disorder (PTSD).

In a Tuesday statement, the US army announced, "The suspect, Sgt John Russell, is charged with five specifications of murder and one specification of aggravated assault."

Meanwhile, the US military proclaimed that it would review its efforts to treat combat stress.

Around a quarter of active American service members frequenting battle zones in Iraq during repeated tours of the region have developed PTSD.

ARQN/SC/AA