The US military has released 198 photographs of alleged abuse in army facilities in Iraq and Afghanistan, with many of the images showing close-ups of cuts and bruises to arms and legs of prisoners.

The American Civil Liberties Union, which filed a Freedom of Information Act lawsuit more than a decade ago for the photos, said the images were part of a larger collection of 2,000 mostly unreleased photographs.

The Pentagon has refused to release additional images, citing national security concerns.

"The still-secret pictures are the best evidence of the serious abuses that took place in military detention centres," ACLU Deputy Legal Director Jameel Jaffer said in a statement.

"The government's selective disclosure risks misleading the public about the true extent of the abuse."

The Pentagon said the photos that were released came from criminal investigations into 56 allegations of misconduct by US personnel more than a decade ago.

It said 14 of those allegations were substantiated and at least one service member was sentenced to life in prison as a result of investigations.

The identities of men in photos are concealed and there is little or no context to suggest exactly how they might have been injured.

Officials declined to provide more information and it was unclear which images were connected to that case, or whether the detainee involved had survived.

None of the images are thought to originate from Iraq's notorious Abu Ghraib prison, where US soldiers were implicated in physical and sexual abuse, infliction of electric shocks, and mock executions.

That scandal first broke when photos showing soldiers abusing detainees were published in US media in 2004.

Between 2004 and 2006, 11 soldiers, including Lynndie England who smiled beside naked prisoners being subjected to sexual abuse, were convicted in court martials.