US lawmakers have been viewing yet more photographs and videos of alleged abuse of Iraqi prisoners by US soldiers.
The unpublished images are reported to include examples of US troops torturing and humiliating captives.
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Senators shown the pictures by Pentagon officials in a closed-door session described them as “disgusting” and “significantly worse” than anticipated.
Earlier it was announced that two more US soldiers are to face courts martial over the alleged abuse.
US officials have rejected any link between the treatment of Iraqis at the notorious Abu Ghraib jail in Baghdad and the beheading of a US hostage.
President George W Bush said there was no justification for the killing of Nick Berg and insisted the US would “complete its mission” in Iraq.
Mr Berg’s killers filmed themselves cutting off his head, saying they were avenging the abuse of Iraqi prisoners.
The CIA is checking claims that top al-Qaeda suspect Abu Musab al-Zarqawi was the killer, as suggested in a video of the beheading shown on an Arabic-language website.
The killing prompted widespread revulsion in the US and around the world.
There had been speculation that the Pentagon would release its entire stock of photos of abuse to minimise the dangers of them leaking out slowly to the media, but correspondents say the killing of Mr Berg and the content of the other images makes this less likely now.
Speaking after seeing the unpublished abuse images, Senator Ron Wyden said : “I expected that these pictures would be very hard on the stomach lining and it was significantly worse than anything that I had anticipated.”
“Take the worse case and multiply it several times over,” he added.
His views were echoed by Senator Dianne Feinstein who said: “The whole thing is disgusting and it’s hard to believe that this actually is taking place in a military facility.”
The latest to be ordered to stand for court martial are Sgt Javal Davis and Staff Sgt Ivan Frederick. Both men are assigned to the 372nd Military Police Company.
The two are alleged to have forced naked prisoners into a pile, which Sgt Frederick then photographed.
Sgt Frederick is also accused of ordering inmates to masturbate in front of other prisoners and guards and of making some of them simulate oral sex while photographing them.
The date for their trials has not been announced.
Another soldier facing trial, Private Lynndie England, said her superiors had ordered her to pose for photographs with naked prisoners.
Speaking publicly for the first time on Tuesday, Private England said that officers had applauded the pictures and told her that the humiliation of the prisoners was paying off.
Defence Secretary Donald Rumsfeld defended interrogation techniques used by the military in Iraq.
He told a Senate committee that methods such as sleep deprivation, dietary changes and making prisoners assume stress positions had been approved by Pentagon lawyers.
The abuse scandal erupted late last month, when photographs displaying the humiliation of Iraqi men in Baghdad’s Abu Ghraib jail were shown by the American media.
CBS television is understood to be going ahead with a broadcast of a video diary by a female American soldier who worked at two prison camps in Iraq.
The video does not show scenes of abuse but the soldier is said to talk flippantly of Iraqi prisoners dying and makes it clear she does not see their safety as important.
“We’ve already had two prisoners die… but who cares? That’s two less for me to worry about,” she is reported to say in the diary.