A senior military official on Friday said the eight new prisoner deaths under investigation had been "classified by medical authorities as homicides, which involve suspected assaults of detainees either before or during interrogation sessions that may have led to the detainees' death."
These deaths are in addition to two homicides of Iraqi prisoners, which the US army earlier this month said had been committed by its soldiers.
The eight additional deaths deemed as homicides were among nine prisoner fatalities that remained under active investigation by the army, the official said.
The Pentagon also released 23 death certificates of detainees who died in Iraq and Afghanistan, including nine suspected homicides.
Among the causes of death listed were multiple gunshot wounds with complications, blunt force injuries complicated by compromised respiration, asphyxia due to smothering and chest compression, and strangulation.
In total, the US army has investigated the deaths of 37 detainees in US custody in Iraq and Afghanistan since August 2002, Pentagon officials said on Friday.
The latest investigations come in the wake of an escalating scandal over the abuse of prisoners by US-occupation troops in Iraq.
Human rights groups say Afghan
detainees have been ill treated
Photographs and videos of American prison guards torturing and sexually humiliating Iraqi inmates at Baghdad's Abu Ghraib prison have surfaced, triggering global consternation.
Sordid tales of abuses emerging from behind the high walls of Abu Ghraib have focused attention on the treatment of prisoners held by US forces.
Despite persistent denials by the United States, human rights groups have since long been expressing concern over the plight of prisoners held by the US forces in places like Iraq, Afghanistan and Guantanamo Bay.
The US government has, meanwhile, opened its first criminal investigation into a civilian contractor in Iraq about possible mistreatment of Iraqi prisoners.
"Yesterday, the Department of Justice received a referral from the Department of Defence regarding a civilian contractor in Iraq, and opened an investigation into the matter," Justice Department spokesman Mark Corallo said on Friday.
"We remain committed to taking all appropriate action within our jurisdiction regarding allegations of mistreatment of Iraqi prisoners," he added.