The U.S. Defence Department will release a "substantial number" of photos depicting abuse of prisoners in Iraq and Afghanistan, the American Civil Liberties Union said late Thursday.

The photos will be made available by May 28, the American Civil Liberties Union said, citing a letter dated Thursday from the U.S. Justice Department to a federal judge in New York City.

The photos' release is in response to a Freedom of Information Act lawsuit filed by the ACLU in 2004 and will include images from prisons in Iraq and Afghanistan at locations other than Abu Ghraib, the ACLU said.

"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," Amrit Singh, staff lawyer with the ACLU, said in a statement.

"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 authorizing or permitting such abuse."

The Justice Department letter, signed by acting U.S attorney Lev Dassin, follows a September 2008 ruling by the U.S. Court of Appeals for the 2nd Circuit requiring disclosure of the photos and the court's subsequent refusal in March 2009 to rehear the case, the ACLU said.

Since the ACLU's FOIA request in 2003, the administration of former president George W. Bush had refused to disclose these images, the ACLU said.

The administration claimed disclosure of such evidence would generate outrage and violate U.S. obligations toward detainees under the Geneva Conventions, the ACLU said.