NEW YORK - Civil libertarians are condemning a call by two influential U.S. senators for the White House to block the impending release of photographs showing detainees being abused by U.S. military personnel at the notorious Abu Ghraib prison in Iraq and at other U.S. detention facilities in the Middle East and elsewhere.

The plea to intervene to stop the expected May 28 release of the photos came in a letter to President Barack Obama from Senators Joseph Lieberman and Lindsey Graham.

"The release of these old photographs of past behavior that has now been clearly prohibited will serve no public good, but will empower al Qaeda propaganda operations, hurt our country's image, and endanger our men and women in uniform," the Senators wrote.

Release of the photos is expected in response to a Freedom of Information Act lawsuit filed by the American Civil Liberties Union.

"We urge you in the strongest possible terms to fight the release of these old pictures of detainees in the war on terror, including appealing the decision of the Second Circuit in the ACLU [American Civil Liberties Union] lawsuit to the Supreme Court and pursuing all legal options to prevent the public disclosure of these pictures," the senators wrote.

Their letter said, "We know that many terrorists captured in Iraq have told American interrogators that one of the reasons they decided to join the violent jihadist war against America was what they saw on al Qaeda videos of abuse of detainees at Abu Ghraib."

As a result of the ensuing actions by Congress, "America's soldiers, sailors, airmen and marines have made great progress in improving detention and interrogation procedures," they wrote.

Senator Graham is a conservative Republican from South Carolina, a member of the Armed Services Committee, and a military lawyer in the U.S. Air Force Reserve.

Lieberman was a lifelong Democrat until he lost his party's primary contest in 2006, after which he ran and won as an Independent from Connecticut. He is chairman of the powerful Senate Homeland Security Committee. The two senators were among the most ardent supporters of the recent unsuccessful presidential campaign of Senator John McCain.

Civil libertarians were virtually unanimous in their opposition to withholding the photographs.

Gabor Rona, international legal director of Human Rights First, told IPS, "Sen. Lieberman and Graham's claims might carry more weight had the U.S. government been consistently honest about the mistreatment it authorised."

"But as long as the American people are kept in the dark about what crimes were committed in their name, they cannot intelligently exercise their democratic right and obligation to call for corrective measures," he said.

Rona added, "To elevate fear of al Qaeda's reactions over faith in our democratic ideals and structures is unfortunate and counterproductive."

Marjorie Cohn, president of the National Lawyers Guild, told IPS, "The more evidence that emerges to document the Bush policy of torture and abuse, the more likely that investigations and prosecutions will take place."

Professor Francis A. Boyle of the University of Illinois Law School told IPS, "The release of these photos will further document torture, abuse and other war crimes inflicted by U.S. military personnel in Iraq, the orders for which go all the way up the military chain of command to the Commander in Chief President Bush, the Secretary of Defence Donald Rumsfeld, and Lt. Gen. Ricardo Sanchez, none of whom has yet been held accountable."

He said, "Senators Lieberman and Graham are simply running interference for all three of them. Yet under the terms of the Four Geneva Conventions of 1949 and the Convention against Torture, the Obama administration has an obligation to open an investigation and to prosecute them. Failure to do so is a war crime in its own right."

"These photographs provide visual proof that prisoner abuse by U.S. personnel was not aberrational but widespread, reaching far beyond the walls of Abu Ghraib," said attorney Amrit Singh of the ACLU, the organisation that originally brought the lawsuit under the Freedom of Information Act (FOIA).

"Their disclosure is critical for helping the public understand the scope and scale of prisoner abuse as well as for holding senior officials accountable for authorising or permitting such abuse," she said.

Lieutenant General Ricardo S. Sanchez, now retired, served as the V Corps commander of coalition forces in Iraq from June 2003 to June 2004. When he retired in November 2006, he called his career a casualty of the Abu Ghraib scandal.

The disagreement over release of the photos reflects conflicting assessments of which is more dangerous and objectionable - the release of the photographs or the abusive behaviour that they depict.

It also turns on unresolved questions concerning the scale of prisoner abuse by U.S. personnel, and the nature of the public accounting that can or should be required.

The original Abu Ghraib photos were first exposed to the public in a 2006 segment of the television program, "Sixty Minutes," and shortly thereafter in an extensive article by investigative reporter Seymour Hersh in The New Yorker magazine.

The images showed Iraqi prisoners hooded, with electrodes attached to their bodies, being menaced by dogs, forced to walk with dog collars around their necks, and made to form pyramids of naked bodies. Existence of the images was first reported by a low-level U.S. Army soldier.

The military conducted more than a dozen investigations of the abusive practices, which then Defence Secretary Donald Rumsfeld attributed to the aberrations of "a few bad apples." A number of low-level soldiers were convicted and sentenced to terms in military prisons, a few others were given official reprimands, and the brigadier general who was in charge of the prison was demoted to colonel.

The Defence Department investigations concluded that no one higher up in the military or civilian leadership of the Pentagon bore any responsibility for the abuses.

While the contents of the new photos have not been made public, it is known that members of Congress viewed them in a classified setting when the original Abu Ghraib images were released. Some have said publicly that the new photos paint an even grimmer picture of prisoner abuse, not only at Abu Ghraib but also at other U.S.-controlled prisons in the Middle East.

It is unclear whether the new crop of photos includes those taken by psychologist Philip Zimbardo. As an expert witness in the defense of an Abu Ghraib guard who was court-martialed, he had access to many of the images of abuse that were taken by the guards themselves.

Zimbardo assembled some of these pictures into a short video. Many of the images are explicit and gruesome, depicting nudity, degradation, simulated sex acts, and guards posing with decaying corpses.

The original Abu Ghraib photos were broadcast around the world long before it became known that U.S. authorities, including the Central Intelligence Agency, were using waterboarding and other "enhanced interrogation techniques" at the Navy detention centre at Guantanamo Bay, Cuba, in Afghanistan, and at secret prisons in Eastern Europe and elsewhere.