Three human rights groups have obtained documents that confirm US Department of Defense involvement in the CIA's "ghost" detention program, and the existence of secret prisons at Bagram air base in Afghanistan and in Iraq.

The documents obtained as part of a long-running legal battle using freedom-of-information laws were released by the Department of Defense to Amnesty International USA, the Centre for Constitutional Rights and the Center for Human Rights and Global Justice last week.

The groups received about 1000 documents from Defence out of more than 12,000 that have been identified as coming within their request but which are still being withheld by agencies including the CIA and the Department of Justice.

The groups said these documents confirm the existence of secret prisons at Bagram and in Iraq; affirm the Defense Department's co-operation with the CIA's "ghost" detention program; and show one case where Defense sought to delay the release of Guantanamo prisoners who were scheduled to be sent home by a month and a half in order to avoid bad press.

The document from the transport division recommended "hold(ing) off on return flights for 45 days or so until things die down. Otherwise we are likely to have hero's welcomes awaiting the detainees when they arrive."

The email also recommended transfer in a smaller, more discreet plane. Around that time a UN report on Guantanamo had been released.

The groups said the documents also revealed that Defence had a policy not to register prisoners with the Red Cross for 14 days and sometimes for 30 days in the interests of collecting intelligence and that this policy was known to the Joint Chiefs of Staff.

"These newly released documents confirm our suspicion that the tentacles of the CIA's abusive program reached across agency lines," said Margaret Satterthwaite, director of New York University's International Human Rights Clinic. "In fact, it is increasingly obvious that Defense officials engaged in legal gymnastics to find ways to co-operate with the CIA's activities."

The head of the Senate Judiciary Committee, Democrat Patrick Leahy, is pushing for the establishment of a "truth commission" answerable to both chambers of Congress to investigate the actions of the Bush administration and departments.

Senator Leahy called his proposal a "middle ground" between those critics of the Bush administration seeking to prosecute officials, and others wishing to concentrate on the future as opposed to investigating the past.

But on Sunday, President Barack Obama was non-committal. While he repeated his line that torture was wrong and would cease under his Administration, he also noted that he was of a mind to look forward not backwards.