A federal judge sentenced a former US Army soldier to life in prison without parole for the gang rape and murder of an Iraqi girl and the slaying of her family in 2006.

Steven Green, 24, was tried and convicted in April as a civilian on murder, rape and obstruction of justice charges because his arrest came after he was discharged from the Army for a "personality disorder."

The former Army private escaped a death sentence when jurors could not agree on his punishment. Judge Thomas Russell of the US District Court in Paducah, Kentucky, handed down the life sentence.

Green led a gang of five US soldiers who invaded the Iraqi family's home in Mahmudiya, 20 miles south of Baghdad, on March 12, 2006, intending to rape the girl, 14-year-old Abeer Kassem Al-Janabi.

While two fellow soldiers assaulted the girl, Green shot and killed the girl's mother, father and six-year-old sister in a bedroom before taking his turn in the gang rape, according to trial testimony. He then shot the girl three times in the head and set her body ablaze.

Of the other four soldiers who took part in the attack, three pleaded guilty and the fourth was convicted in military courts. They received prison sentences ranging from five to 100 years.

The case was one of several incidents involving US soldiers that enraged Iraqis and strained US relations with the country and its government.

"We sincerely hope that today's sentencing helps to bring the loved ones of this Iraqi family some semblance of closure and comfort after this horrific and senseless act," Brigadier General Rodney Johnson, the Commanding General of the US Army Criminal Investigation Command said in a statement.

Green's case was heard in Paducah, in western Kentucky, because of its proximity to Fort Campbell, where he was based.

Relatives of the slain Iraqi family travelled to Paducah after Green's trial and condemned him as a "coward" who would be haunted by his acts.

"The face of this innocent girl, that face will be chasing you in that dark cell you will be in until the last day of your life," the girl's uncle said at the court hearing.