An Iraqi group linked to al-Qaeda has released a video appearing to show the mutilated bodies of two US soldiers.
The two went missing in mid-June and were found dead days later
The Mujahideen Shura Council said it had captured and killed the soldiers in revenge for the alleged rape and murder of a young Iraqi woman by US troops.
Kristian Menchaca and Thomas Tucker were seized from a checkpoint to the south of Baghdad on 16 June.
The US had previously said there was no link between the soldiers' deaths and the alleged rape and killing.
A US institute that monitors extremist video releases said the film - published on the internet - showed "extremely graphic footage" of the two men's corpses.
Both bodies were reported to have been mutilated, matching reports by US authorities who said the two bodies recovered last month showed signs of "barbaric torture".
In a statement, the US military strongly condemned the video, insisting those responsible would be "brought to justice".
"It demonstrates the barbaric and brutal nature of the terrorists and their complete disregard for human life," the statement said.
According to the Site Institute, the video was preceded by previously-released audio clips from al-Qaeda's leader Osama Bin Laden and the former leader of al-Qaeda in Iraq, Abu Musab al-Zarqawi.
The seizure of the two soldiers last month at a checkpoint near Yusufiya sparked an extensive US military search.
However, their bodies were recovered days after their disappearance.
The Mujahideen Shura Council, which represents insurgent groups in Iraq, said in a statement it had abducted the men and slit their throats.
In the newly-released film, the captors linked their actions directly to the rape and killing of the Iraqi girl and her family in the town of Mahmudiya.
The groups said capturing and killing the soldiers was "revenge for our sister who was dishonoured by a soldier of the same brigade".
A criminal investigation began on 24 June and four US soldiers on active duty and one former soldier, Steven Green, have been charged with murder, as well as with the rape of one of the family members.
A fifth soldier serving in Iraq has been charged with dereliction of duty for not reporting the offences.