Most serious charge carries a mandatory minimum sentence of 30 years.
Five guards with private US security firm Blackwater were charged Monday with 35-counts of manslaughter, attempted manslaughter and weapons violations in the deaths of 17 Iraqis who were gunned down in a Baghdad square, the Justice Department said Monday.
The accused face up to 10 years in jail on each of 14 manslaughter charges and seven years for each of 20 counts of attempted manslaughter, said Jeff Taylor, attorney for the District of Columbia.
The weapons violation of "discharging a firearm and destructive devices during a crime of violence" carries the stiffest sentence - a mandatory minimum of 30 years in prison, he said.
In addition to the five guards who were indicted, a sixth guard has "pleaded guilty to charges of voluntary manslaughter and attempt to commit manslaughter for the same shooting in Baghdad, Iraq," said Justice Department spokesman Patrick Rowan.
According to the indictment, the accused were on patrol with a convoy of trucks when they opened fire with automatic weapons on unarmed civilians in a square in Baghdad on Sept. 16 last year.
Fourteen Iraqis were killed and 18 wounded, according to the indictment.
"None of the victims of the shooting was armed," said Taylor.
"None of them was an insurgent. Many were shot while inside civilian vehicles attempting to flee. One victim was shot in the chest while standing in the street with his hands up," he said.
"While there were dangers in Baghdad in September 2007, there were also ordinary people going about their lives, performing mundane, daily tasks," said Rowan.
"For the safety of these people, as well as US government personnel and their own colleagues, security guards were obligated to refrain from firing powerful weapons," he said.
Blackwater said in a statement that all its personnel "operate according to strict rules for use of force issued by the US government."
"Based on the information available to us... we understand that these individuals acted within the rules set forth for them by the government and that no criminal violations occurred," the company said.
But, it added, if any individual is determined to have acted improperly, "then Blackwater supports holding that person accountable."
The charges were the first to be brought under the Military Extraterritorial Jurisdiction Act (MEJA) against private contractors, according to Taylor.
MEJA, which was passed in 2000, gives the US judicial system the "ability to exercise jurisdictional control over American civilians committing felonies on foreign soil," according to an official at the Pentagon.
Blackwater's contract to provide security services to US and foreign diplomats in Iraq was renewed earlier this year by the US State Department, against the wishes of the Iraqi government.
The Iraqi authorities have said they may seek to bring the six Blackwater guards charged Monday to trial in Iraq.
"The Iraqi government stresses its rights and that Blackwater guards have committed crimes against Iraqi victims. The government reserves the right to prosecute them," government spokesman Ali Al-Dabbagh said in August.
The five accused guards turned themselves in, in the southwestern state of Utah, where they are due to appear in court later Monday, the officials said.