Master Sergeant Lisa Girman, 35, was the most senior person in charge during the incident at Camp Bucca in southern Iraq. She knocked a prisoner to the ground and repeatedly kicked him in the groin, abdomen and head, encouraging subordinate soldiers to do the same.

Another of the three, Scott McKenzie, 38, dragged a prisoner by his arms across the ground and, holding his legs apart, encouraged soldiers to kick him in the groin, abdomen and head. McKenzie then threw the prisoner to the ground and stepped on his injured arm.

Timothy Canjar, 21, held a prisoner's legs apart while others kicked him in the groin, and violently twisted his already injured arm.

The three soldiers, all from Pennsylvania, have been sent back to America after months of investigations led to their administrative discharge by Brigadier-General Ennis Whitehead III, the acting commander of the 143rd Transportation Command. The investigation began after soldiers who witnessed the abuses reported them.

The soldiers had been facing a court-martial proceeding, but agreed instead to a non-judicial one. In addition to the discharges, two soldiers had their ranks lowered, and all three were ordered to forfeit pay for two months.

"The charges stem from an incident last year when prisoners were being moved. Master Sergeant Girman, who was the senior person and in charge, was charged with physical abuse of Iraqi detainees," Lieutenant-Colonel Vic Harris told Reuters.

McKenzie and Canjar were also convicted of making false sworn statements to army investigators. The soldiers said they acted in self-defence.

Allegations of mistreatment of prisoners of war have also been levelled at a high-profile British army officer during the war, but he was cleared by the Ministry of Defence.

The ministry ordered an investigation into Col Tim Collins, the former commanding officer of the 1st Battalion, Royal Irish Regiment, following a US major's allegations of abuse of captured Iraqis.

· The US military yesterday released three Iraqi employees of Reuters news agency and an Iraqi cameraman of the US network NBC who were detained on Friday after an American helicopter was shot down, a military official said.

Shortly after the incident, in which a US soldier was killed, the military said its troops in the area had been fired upon by assailants posing as journalists, and that it had detained four suspects.

The US military has said it was investigating, and has not commented on the possibility that soldiers mistook the journalists for guerrillas.