"It seems to me that it's far more likely that a group of out-of-control, undisciplined guards would beat up prisoners, not strip them naked and put them in a human pyramid," Collins said. Both Taguba and Lt. Gen. Lance Smith, deputy commander of U.S. Central Command, which oversees military operation in Iraq, said that the photographs of abuse were taken by digital cameras that belonged to individuals, suggesting that they were not part of an interrogation plan.

Warner, though, said he understood that the photographs were to be shown to prisoners' families as a threat.

On Tuesday, a CIA official said the agency's inspector general's office is conducting three investigations into allegations of wrongdoing involving actions in Iraq. One of the incidents occurred at Abu Ghraib, the official said, and the others were in Afghanistan and Iraq.

The official, who spoke on condition of anonymity, confirmed earlier reports that the victim at the prison was an Iraqi officer who died while being questioned and that CIA officers had denied any mistreatment.

At the White House, spokesman Scott McClellan said that the president was briefed on Taguba's report last week and watched some of Tuesday's testimony on television.

"He wants it to be an open and transparent process, so that the world knows that when allegations like this...come to light, that America acts swiftly to bring people to justice," McClellan said.

From its headquarters in Geneva, UNICEF, the U.N. children's agency, issued a statement that it was "profoundly disturbed by news reports alleging that children may have been among those abused" in Iraq detention facilities.

According to news reports, there are allegations that boys were raped at the Abu Ghraib prison and that some children may have been tortured during interrogations.

Also Tuesday, the American Civil Liberties Union released a letter urging President Bush to comply with its seven-month-old Freedom of Information Act request on allegations of torture of detainees.

"Abu Ghraib wasn't the result of a couple of lone sadists in the military — it was a direct and easily foreseen consequence of detention policies that lack transparency and safeguards against this type of abuse," ACLU Executive Director Anthony Romero said in a statement.

Meanwhile, at the Pentagon, a senior officer led a town hall meeting by praising Rumsfeld, who has been under attack.

"There's not a single human being in this government, and certainly, not in this building, who works harder or is more dedicated, or is a better patriot than is secretary Rumsfeld," said Gen. Peter Pace, vice chairman of the Joint Chiefs of Staff. "It's my great honor and distinction to serve on his team. I'd ask you to join me in thanking him for his leadership."

Many Democrats and newspaper editorials have recently called for Rumsfeld to resign over the prisoner abuse scandal.

Rumsfeld said last week that he would not remain in the job if he did not believe he could continue to be effective. Since that time, President Bush has praised him and said the "nation owes him a debt of gratitude."