Pentagon officials have revealed eight more investigations into the suspected murder of prisoners in US custody.
Most of the cases took place in US detention centres
The new inquiries bring to 37 the number of detainee deaths in Iraq and Afghanistan which under examination by US officials. Ten of the deaths are categorised as homicide.
Several prisoners were found to have died before or during interrogation.
Two detainees died at Abu Ghraib prison in Baghdad which is at the centre of allegations of abuse by US soldiers.
In a separate announcement, the US Department of Justice said it had opened the first criminal investigation of a civilian contractor for alleged mistreatment of prisoners in Iraq.
Thirty-two of the deaths under investigation took place in Iraq and five in Afghanistan. Some of the deaths date back to August 2002.
Most of the detainees died inside detention facilities and around half of the deaths have been attributed to natural causes.
Other causes of death given include:
- multiple gunshot wounds
- blunt force injuries and asphyxia
force injuries complicated by compromised respiration
- pulmonary embolism due to blunt force
injury to the legs
Two weeks ago, the Pentagon announced that two investigations had concluded that prisoners had been murdered.
An army official said a soldier had been convicted of using excessive force when he shot dead a prisoner who was throwing stones at him.
He was thrown out of the army but did not go to jail.
The other murder was committed by a private contractor who worked for the CIA, the official said.