A U.S. official says Army Staff Sergeant Robert Bales, accused of killing 17 Afghan civilians during a March 11 shooting spree in two villages in southern Kandahar province, will be charged with 17 counts of murder.

The official, speaking on condition of anonymity, said Thursday the 38-year-old father of two will also be charged with six counts of attempted murder and six counts of assault.

Bales, an 11-year military veteran, is alleged to have walked out of his southern Afghanistan military post under cover of darkness and gunned down nine children and eight adults. He is being held in an isolated cell at a military prison at Fort Leavenworth, in Kansas.

The incident was yet another blow to already shaky U.S.-Afghan relations, following a series of missteps, including the inadvertent burning of Qurans at a U.S. military base near Kabul.

Bales' civilian lawyer, John Henry Browne, indicated his client was likely suffering from combat stress and post-traumatic stress disorder.

Bales, who served three tours of duty in Iraq before being sent to Afghanistan last December, suffered a traumatic brain injury in Iraq in 2010. A day before the massacre, he witnessed one of his fellow soldiers get his leg blown off.