WASHINGTON — US Army Staff Sergeant Robert Bales is likely to be formally charged in the next few days with the shooting deaths of 16 Afghan villagers, an American military official told AFP on Monday.

Bales, 38, is accused of leaving his base in the Panjwayi district of Kandahar province on the night of March 11 to commit the killings, which included nine children. He allegedly set several of their bodies on fire.

The soldier -- who prosecutors say returned to his base and turned himself in to authorities after the incident -- faces the possibility of the death penalty if convicted, according to US Defense Secretary Leon Panetta.

Under the US military justice system, prosecutors draft charges to be filed against an accused soldier, then present them to his unit commander, who must then decide whether there is enough evidence to believe a crime was committed.

If so, the commander signs the charging documents so that the case can be "preferred" for formal prosecution.

"My understanding is that the preferral of charges on Sergeant Bales will be announced by (his commanding officer in) Afghanistan," the US Army official told AFP.

"I expect it to be within the next few days. It is that point in time when a suspect is formally charged."

Before trial, Bales must appear at an "Article 32" hearing -- a preliminary hearing at which prosecutors argue for a court-martial.

The attack plunged US-Afghan relations into deep crisis, with Afghan President Hamid Karzai stating that international forces should leave villages in his country.

Bales initially was sent to a military base in Kuwait then transferred to the US military prison at Fort Leavenworth, Kansas, where he is kept in isolation in a cell, according to Army officials.

Bales met his civilian attorney, John Henry Browne, at the base on Monday, Fort Leavenworth public information officer Jeff Wingo told AFP.

Browne said last week that Bales had recently been under stress, which was heightened when he witnessed a fellow soldier seriously wounded by stepping on a mine. He did not explain the legal defense he would use for his client.

The US media reported that Bales, who in addition to Browne also has a military lawyer, and his wife were enduring financial problems.

The non-commissioned officer, who joined the Army two months after the September 11, 2001 terrorist attacks, served three tours of duty in Iraq and had been in Afghanistan since December.