Two of the soldiers could face the death penalty if found guilty.

Seven other personnel are to face court martial over deaths in two separate cases, in north Iraq and in Hamdaniya.

Separately, President George W Bush in a TV interview acknowledged for the first time a parallel between Iraq and the Vietnam War.

Combat stress

The three court martial cases are further straining the relationship between the US and the Iraqi government, says the BBC's James Coomarasamy in Washington.

The first group, all soldiers from the 2nd Brigade of the elite 101st airborne division, were at the time serving in Mahmudiya, about 20 miles (32km) south of Baghdad.

They are charged with premeditated murder and rape. Three are also charged with arson and housebreaking.

The military said Sgt Paul Cortez and Pfc Jesse Spielman could face the death penalty if found guilty, while Spc James P Barker and Pfc Bryan L Howard could face life-long jail terms.

The men are alleged to have helped a former private - Steven Green, who has since left the army - plan, carry out and cover up the attack.

Mr Green has pleaded not guilty in a federal court and will be tried separately in the US.

At hearings during the investigation, colleagues of the accused described intense combat stress, with troops left demoralised and emotionally drained by frequent insurgent attacks.

Propaganda

In the second case, four soldiers from the 3rd Brigade of the same division have been referred to court martial on murder charges.

President Bush's allusion to Vietnam may raise eyebrows

Sgt Raymond Girouard, Spc William Hunsaker, Spc Juston Graber and Pfc Corey Clagett are accused in the shooting of three male Iraqi prisoners near Tikrit, Salahuddin province, in northern Iraq.

The detainees died during a US military operation near the Thar Thar Canal near Tikrit on 9 May 2006.

The cases are two of several in which US soldiers serving in Iraq have been accused of abuses against Iraqis.

No dates have been set for the courts martial.

In his TV interview, Mr Bush agreed that the situation in Iraq could be compared with the 1968 Tet offensive in Vietnam, where the North Vietnamese inflicted a huge psychological blow on the Americans and their allies.

"There's certainly a stepped-up level of violence," Mr Bush said.

The White House later said Mr Bush was referring to propaganda and that the "enemy is trying to shake our will".

The BBC's Justin Webb in Washington says that although Mr Bush appeared to be suggesting that steadiness of nerve could avoid a repeat of history, any comparison with Vietnam will raise eyebrows.