The Obama Administration is to release up to 2,000 photographs showing the abuse of prisoners in Iraq and Afghanistan, a move that will intensify pressure on the White House to back the prosecution of Bush-era officials for authorising alleged torture.

The release of the pictures, forced on the White House by a freedom of information lawsuit lodged five years ago, will complicate President Obama's desire to move on from the abuse issue, which has begun to bedevil his presidency. The images are proof that the brutal treatment of detainees went far beyond the Abu Ghraib prison scandal in Iraq. They must be made public by May 28.

The leading anti-torture envoy at the United Nations stoked the controversy by insisting that the US was obligated by the UN's Convention on Torture to prosecute lawyers in the Bush Administration who justified harsh interrogations.

For the first time the photographs are believed to provide images of abuse at Guantánamo Bay, as well as at facilities in Iraq and Afghanistan. According to US officials who have seen the pictures, some show American service members intimidating prisoners by pointing weapons at them, an offence that in the past has brought courts martial.

One official said that the pictures were not as shocking as those that emerged from Abu Ghraib but were “not good”. The Abu Ghraib photographs showed Iraqi prisoners hooded, intimidated by dogs, beaten and piled naked in sexually embarrassing positions.

Since his decision to release four CIA torture memos last week that detailed the harsh interrogation techniques approved by the White House under President Bush, Mr Obama and his aides have faced anger from both liberals and Republicans.

The move dismayed officials inside the CIA, despite Mr Obama's initial assurance that neither CIA agents nor Bush-era policymakers would face prosecution.

Then this week Mr Obama appeared to raise the possibility of the possible prosecution of officials. That triggered such an uproar from Republicans, led by the former Vice-President Dick Cheney, who is calling for more documents to be declassified to prove that methods including simulated drowning worked, that Mr Obama has retreated from the idea.

Mr Obama said on Thursday that he did not favour congressional hearings or a “truth commission” into alleged abuses, but he has no power to block such moves on Capitol Hill. Momentum is rapidly building there for bringing senior members of the former Administration before House and Senate committees.

Liberals, meanwhile, are expressing anger that Mr Obama is not backing prosecutions, and the release of the new photographs will increase their demands for retribution.

Amrit Singh, a lawyer for the American Civil Liberties Union, which brought the freedom of information lawsuit, said of the photographs: “This will constitute visual proof that, unlike the Bush Administration's claim, the abuse was not confined to Abu Ghraib and was not aberrational. This 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.”

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