The Pentagon yesterday said it would release hundreds of photographs from investigations into prisoner abuse but insisted they did not reveal a policy of mistreatment.

The Obama Administration's commitment to release the pictures by May 28 could fan the flames of a political firestorm over the treatment of terrorism suspects and other detainees during George W. Bush's presidency.

Defence Secretary Robert Gates voiced concern this week that publicising details of US interrogation practices and photographs of prisoner treatment could trigger a backlash against US troops in Iraq and Afghanistan.

The American Civil Liberties Union has spent years suing the government for the release of the pictures, which came from military investigations. The group said they showed prisoner abuse went far beyond well-known cases in Iraq and elsewhere.

"These photographs provide visual proof that prisoner abuse by US personnel was not aberrational but widespread," said Amrit Singh, an ACLU lawyer. No details have yet been released of what the pictures show. The Pentagon said its policy had always been to treat detainees humanely and the investigations that yielded the photographs showed the US military did not tolerate abuse.

"What this demonstrates is that we have always been serious about investigating credible allegations of abuse," Pentagon spokesman Bryan Whitman said.

He said more than 400 military personnel had been disciplined for failing to follow detainee policies. Their punishments in-cluded prison sentences, bad conduct discharges and demotions, he said.

Mr Whitman said the Pentagon decided to release the pictures after courts twice ruled in the ACLU's favour. "We felt this case had pretty much run its course," he said. "Legal options at this point had become pretty limited."

The Pentagon has long argued that abuse at Abu Ghraib jail outside Baghdad following the 2003 US invasion, which came to public attention when shocking photographs were released in 2004, and other high-profile cases were isolated incidents.

Rights groups and congressional investigators say the abuse was linked directly to policies approved by Bush Administration officials, including former defence secretary Donald Rumsfeld, and that low-level soldiers were made scapegoats.

Mr Whitman said the Pentagon would release 44 photos already identified in the court battle with the ACLU, along with a substantial number of others. A US defence official said the number of pictures released would be in the hundreds.

Some pictures would be redacted to protect the identity of those involved, Mr Whitman said. Several US courts had already ordered the release of some of the pictures.

The decision to release the images comes amid a fierce debate over the Obama Administration's release last week of Bush-era memos sanctioning harsh interrogation methods on terrorism suspects.

The methods include waterboarding, a form of simulated drowning, sleep deprivation and forced nudity.

"I think pretending that we could hold all of this and keep it all a secret even if we wanted to... was probably unrealistic," he told reporters at Camp Lejeune, a Marine Corps base in North Carolina. "So we'll just have to deal with it.

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