Following on from Friday's all-day grilling of Defence Secretary Donald Rumsfeld, the Senate Armed Services Committee will first hear from US Army Major General Antonio Taguba on Tuesday, who wrote a report outlining the abuses.
On Tuesday afternoon, the committee will question Under Secretary of Defence Stephen Cambone, who is in charge of intelligence, and other Pentagon officials about the scandal that has sparked international outrage and calls from Democrats for Rumsfeld's resignation.
In his report, completed in March, Taguba cited the "systematic and illegal abuses of detainees," and said between October and December 2003, "numerous incidents of sadistic, blatant, and wanton criminal abuses were inflicted on several detainees."
Senator Richard Durbin, an Illinois Democrat, said Taguba's report described "in sickening detail" the cases of mistreatment that also were shown through graphic photographs televised around the world of naked prisoners stacked in a pyramid or positioned to simulate sex acts at the Abu Ghraib prison.
The hearings come as the Congress prepares to see a new set of photographs and a video that Rumsfeld warned may be even more shocking.
Senate Armed Services Committee Chairman John Warner, a Virginia Republican, asked the Pentagon to hold off on delivering the classified material until legal questions are answered on how it could affect criminal investigations, privacy protections and other issues, his spokesman said.
There also are questions on how the handover of the materials to the Senate would affect their classified status, said spokesman John Ullyot.
"Before the Senate comes into receipt of this material, it needs to examine all of the implications," he said, adding that both Republican and Democrat counsel for the Senate leadership and the Armed Services Committee were reviewing it.
Rumsfeld is under pressure to
resign following abuse reports
Warner's committee might have another hearing on Thursday on the Iraqi prisoner abuses, Ullyot said, but witnesses had not been set.
"Senator Warner said the Armed Services Committee would pursue this no matter how embarrassing the results," he said.
The Senate on Monday unanimously passed a bipartisan resolution condemning the mistreatment. It also said the government should conduct a full investigation of abuses and take measures to see they do not happen again, with oversight by congressional committees.
Bush sees photos
President George Bush was shown a "representative sample" on Monday of the hundreds of photographs of abuses of Iraqi prisoners by US soldiers that have not yet been seen by the US public, a senior defence official said.
More than a dozen large, colour prints of photographs of abuse taken at Abu Ghraib prison in Iraq were shown to Bush in Rumsfeld's office after an hour-long briefing at the Pentagon on the situation in Iraq, officials said.
More pictures of abuse have not
yet been made public
"The president's reaction was one of deep disgust and disbelief that anyone who wears our uniform would engage in such shameful and appalling acts," White House spokesman Scott McClellan said.
"It does not represent our United States military and it does not represent the United States of America," he said.
A senior defence official, who spoke on condition of anonymity, said Rumsfeld showed Bush "a kind of representative sample" of images selected from hundreds of photographs of Iraqi prisoners being abused.
"He showed him kind of a range of the activities that are available," the official said.
Among the pictures shown to the president were stills taken from videos but not the videos themselves, McClellan said.
Larry DiRita, the Pentagon's chief spokesman, told reporters that in addition to the photographs, the Defence Department has in its possession a couple of dozen short videos of varying quality that also show abuses being committed.
"They were disturbing. There are some involving humiliation of a nature we've already seen ... There is clearly inappropriate behaviour, including some inappropriate behaviour of a sexual nature"
Pentagon's chief spokesman
He said there were "many, many hundreds" of images on three CD-Roms, but noted that each disc contained many duplicate images so the total number was difficult to determine.
DiRita, who has seen the images, said they were "broadly consistent" with the findings of an investigation by Major General Antonio Taguba into the abuses.
Taguba found among other things that prisoners were beaten, slapped and kicked; that female as well as male detainees were photographed and videotaped naked; that a guard had sex with a female detainee; that prisoners were sodomised with chemical lights; groups of male detainees were forced to masturbate while being videotaped; that photographs were taken of dead detainees.
It was unclear from his report whether those abuses were all captured in photographs or videos.
"They were disturbing. There are some involving humiliation of a nature we've already seen," DiRita said of the images.
"There is clearly inappropriate behaviour, including some inappropriate behaviour of a sexual nature," he said.
The question of whether to make a public release of the images was discussed at the Pentagon briefing, McClellan said, adding that the Pentagon was weighing the impact on privacy concerns and on ongoing criminal investigations.
"They also believe it is very important to keep Congress informed about these matters. Congress has an important oversight role to play," he said.
DiRita said discussions with members of Congress was on whether to release the images to the public, and if so how.
"But the emphasis right now is whether," he said. However, he said, "we haven't ruled it in or out."