Senators examining the Abu Ghraib prison scandal criticized the CIA (search) on Thursday for failing to provide Army investigators with documents on unregistered "ghost detainees."

At a hearing, lawmakers indicated their frustration that Army generals who investigated the prison abuses couldn't put a specific figure on the number of ghost detainees and could only give a range of up to 100 detainees, though they said it was more likely closer to two dozen.

"It's a very difficult question for us to answer, Mr. Chairman, because we don't have the documentation," Gen. Paul Kern, who oversaw an Army investigation of the 205th Military Intelligence Brigade, told Senate Armed Services Committee Chairman John Warner, R-Va.

The panel's top Democrat, Sen. Carl Levin of Michigan, said "it's totally unacceptable that documents that are requested from the CIA have not been forthcoming." And, Sen. John McCain, R-Ariz., said the ghost detainee (search) issue "needs to be cleared up really badly."

Contacted after the hearing, CIA spokesman Mark Mansfield declined to comment on number of ghost detainees and said it is one aspect of a review under way by the agency's inspector general.

At sessions before the Senate panel and its House counterpart, generals also touted reforms the Defense Department has made since the start of the scandal.

"If you visited Abu Ghraib (search), if you visited with our soldiers, you would see a very, very different picture" now, Kern said.

But Democrats pushed for more answers on how the mistreatment happened and who is to blame.

"This committee is still missing significant information necessary to fully understand where responsibility lies," Levin said.

So far, only low-level military service members have been charged in the abuses, though blame goes up the chain of command and some responsibility originated at the Pentagon, said Rep. Ike Skelton of Missouri, ranking Democrat on the House Armed Services Committee.

"It's time to get to the top of this problem," he said.

Harold Brown, a former defense secretary and a member of one of several groups that investigated the abuses, said the entire Bush administration bears some responsibility, including for failure to send enough troops to handle the large prison population and sowing confusion over whether the Geneva Convention applied to prisoners taken in the war on terror.

"Clearly, responsibility for failing to plan for what actually happened after the overthrow of Saddam Hussein extends all the way to the top — obviously (to) the office of the secretary of defense, " Brown told the House panel. "But it goes beyond that. It's true of the whole administration."

Critics have for months said fault may ultimately rest with White House and Pentagon leaders for creating confusion when they decided in early 2002 that terrorist suspects at Guantanamo Bay did not fall under Geneva Conventions and then sought to redefine longtime rules of detention, interrogation and trials to suit the counterterror war.

The Pentagon is under increasing fire for its handling of the prison abuse investigation, as some retired military officers call for an independent commission to get to the bottom of the four-month-old scandal.

The Pentagon says a probe headed by former Defense Secretary James Schlesinger (search) — on which Brown was a member — was independent, but its members were appointed by Defense Secretary Donald H. Rumsfeld, who has been criticized in the scandal.

An Army investigation headed by Maj. Gen. George Fay (search) concentrated on which military intelligence officers at Abu Ghraib prison in Iraq (search) could be charged with crimes under military law. But Fay's group also said the Army's top commanders in Iraq shared some blame for management failures.

The Schlesinger report looked at Afghanistan and Guantanamo Bay (search) as well as Iraq and at military police, the Joint Chiefs of Staff and Rumsfeld as well as intelligence officers in Iraq. It concluded that while lower ranking soldiers might be charged, some blame could go to the highest levels of the Pentagon for inadequate supervision and failure to adapt to developments.

The scandal created international revulsion four months ago with disclosure of photographs showing troops threatening prisoners at Abu Ghraib with dogs, posing them in sexual positions and keeping detainees naked and hooded.

Though defense officials said the photos portrayed the actions of a few bad apples, the controversy has grown to include probes of some 300 allegations of detainee deaths, torture or other mistreatment, some during interrogations to gather intelligence.

Abuses occurred as long as nearly two years ago — among prisoners taken in the campaign to rout Al Qaeda (search) from Afghanistan.