"I think command responsibility has to be looked at just as seriously as the abusers," Republican Sen. Lindsey Graham of South Carolina said in an interview. "The culture that led to this outrageous conduct has to be addressed just as much as the conduct itself."

Sen. Ben Nelson, D-Neb., added: "I think we need to move beyond scapegoating here of privates and sergeants to get at the facts as to what truly did happen."

Both lawmakers, members of the Senate Armed Services Committee, said testimony from Defence Secretary Donald Rumsfeld on Friday helped answer some questions, but many remain about the photographed abuse by US soldiers at the Abu Ghraib prison.

While Massachusetts Sen. Edward Kennedy and other prominent Democrats have called for Rumsfeld to resign, Nelson said he wasn't yet ready to go that far.

The investigation needs to run its course, he said, but he cautioned that, "I may get there depending on what other information comes out."

As for whether Rumsfeld will survive the scandal with his job, that is "still up in the air," said Nelson. "What I'm hearing is that there is a genuine concern about his ability to perform in his office in the way that he needs to."

Those urging President Bush to fire his defence chief should proceed carefully, Graham said, maintaining that Rumsfeld can still be an effective leader.

"I hope people will understand that replacing a secretary of defence during a war is a very big deal and should be done with lots of concern and caution," Graham said.

Rumsfeld warned of more horrific images of prisoner abuse to come, but Nelson and Graham both said they have not seen the additional photos and video that the secretary alluded to during his testimony.

Graham said there have been allegations of rape and murder at Abu Ghraib, and that it would not be far-fetched to fear additional pictures may show such crimes.

Sen. Bob Bennett, R-Utah, said Saturday he assumes Rumsfeld's job is safe. "I certainly hope it is," he said during a break at the Utah GOP convention. "And I don't think there needs to be a congressional investigation."

But Rep. Jim Matheson, Utah's only Democrat in Congress, said at his party's convention that "we have to hold people accountable. This was kept from Congress for a number of months. That bothered me."

Rep. Rick Larsen, D-Wash., said Friday: "In order to protect our women and men in the military, we need to fully prosecute the individuals who perpetrated these acts. We must also hold accountable those who allowed these events to occur from the top to the bottom of the chain of command."