The official says charges against Bales also include six counts of attempted murder and six counts of aggravated assault and other violations of military law. The official spoke on condition of anonymity because the charges had not been announced.
Bales allegedly gunned down nine Afghan children and eight adults as they slept. The 10-year Army veteran remains in custody in a military prison at Fort Leavenworth, Kansas.
The death toll in the shooting rampage at an Afghan village was raised earlier Thursday from 16 to 17. The U.S. Defense Department did not explain the change in the number of victims.
The Pentagon disputes claims by Afghans that the rampage was in retaliation for a roadside bombing of a U.S. military vehicle days before the massacre.
U.S. officials announced that the soldier's trial will be held in the U.S. Afghan officials have asked for some role in the criminal proceedings, perhaps as observers, and to be kept up to date on the process of the case.
President Hamid Karzai has not demanded that Bales be turned over to the Afghan justice system, although some in the country's parliament did.
The Associated Press contributed to this report.