US Army Staff Sergeant Robert Bales, accused of killing Afghan civilians in a shooting rampage in Kandahar province last week, will be charged with 17 counts of murder, a US official said on Thursday.
Earlier accounts of the incident, which has damaged US-Afghan relations, had tallied 16 victims, including nine children and three women.
Bales, a four-tour combat veteran, will also face other charges, including attempted murder, but the official was unable to say how many additional counts there would be.
Legal proceedings would likely take place at Bales' home base, Joint Base Lewis-McChord, close to Tacoma, Washington, the US official said.
Bales, 38, is being held in solitary confinement at a military detention center in Leavenworth, Kansas. His civilian defense attorney, Seattle-based John Henry Browne, was not immediately available for comment.
Earlier this week, Browne said US authorities had no proof of what occurred on the evening in question, and that Bales had "no memory" of the incident.
Browne, who has defended several multiple homicide suspects, including serial killer Ted Bundy, has indicated that stress may have played a role in his client's state of mind.
He is expected to evoke post-traumatic stress disorder, or PTSD, as a factor in the trial, a technique he employed in the defense of a Seattle-area thief known as the "Barefoot Bandit." The US Army said this week it was reviewing the way it diagnoses PTSD among troops.
Browne has said that Bales drank alcohol on the night of the shooting, but not enough to impair his judgment. He has denied that marital or financial problems may have negatively affected Bales, but he said his client was not happy at being sent on his fourth war-zone deployment after three tours of duty in Iraq, where he suffered two wounds.
Browne has played down the effect of Bales' financial problems, which include an abandoned property in the Seattle area and an unpaid $1.5 million judgment from his time as a securities broker.
Bales' wife, Karilyn, is being sheltered by the Army at Lewis-McChord.