A US Army sergeant is to face court martial on Monday on murder charges, with media reports accusing him of taking part in the killing of bound and blindfolded Iraqi prisoners near Baghdad.
Sergeant First Class Joseph P Mayo has been charged with premeditated murder, conspiracy to commit premeditated murder, and obstruction of justice, according to an army statement.
He was one of seven soldiers implicated in the case, and one of three non-commissioned officers to be tried for murder.
Co-defendant Sergeant Michael P Leahy, an army medic, has pleaded guilty and was sentenced in February to life in prison with the possibility of parole.
Master Sergeant John E Hatley has also been accused of taking part in the killings of four Iraqi prisoners in March or April 2007, and is to stand trial on April 13, an army statement said last week.
Hatley faces similar charges "stemming from a separate incident that occurred in early January 2007," it added.
All the soldiers were with the 1st Battalion, 18th Infantry Regiment, 2nd Brigade of the 1st Infantry Division in Iraq, which is now part of the 172nd Infantry Brigade based in Germany.
Mayo's trial is to be held at an army court in the small town of Vilseck, southern Germany, and Hatley is to be tried there as well.
Two other soldiers have pleaded guilty to lesser charges and been sentenced to prison terms of less than a year, US media reports said, while the army has dropped criminal charges against two other sergeants, an army spokeswoman said.
According to media reports, Hatley, Mayo and Leahy allegedly killed four Iraqi prisoners with pistol shots to the head and dumped their bodies into a Baghdad canal, after attacks on a US patrol killed two soldiers.
US military law forbids harming enemy combatants once they are disarmed and in custody.
The New York Times quoted statements and court documents in which Mayo and Leahy each told of killing at least one of the Iraqi detainees on instructions from Hatley.
The Times said it had obtained the documents from someone close to a soldier in the unit who insisted on anonymity and who had an interest in the outcome of the legal proceedings.
According to those documents, the US soldiers detained the Iraqis following a firefight and seized automatic weapons, grenades, and a sniper rifle, but were told by superiors to release the men for lack of sufficient evidence.
A soldier in the US unit had previously been killed by a sniper, and another by a roadside bomb, the report said.
Several US troops have already faced trial in connection with alleged or proven killings in Iraq, at courts both there and in the United States.
In one case, eight US Marines were initially charged in connection with the deaths of 24 Iraqi civilians in the town of Haditha, west of Baghdad, in November 2005.
So far, at least seven of the accused have either been acquitted or had charges withdrawn before court martial.
In another case involving the rape and murder of a 14-year-old Iraqi girl and the killing of her father, mother and younger sister, four soldiers were convicted by a court martial and handed sentences of up to 110 years in prison.
The last defendant, Steven D Green, is to be tried next month in a civilian court in Paducah, Kentucky and could face the death penalty if convicted.