Obama defends 'absolution' of CIA

The techniques included slamming detainees against walls, waterboarding them and keeping them naked and cold for long periods.

In releasing the documents, the most comprehensive accounting yet of interrogation methods that were among the Bush administration's most closely-guarded secrets, Mr Obama said he wanted to move beyond "a dark and painful chapter in our history".

Human rights groups and many Obama officials have condemned such methods as torture.

Past and present CIA officials had pressed unsuccessfully for more parts of the four legal memos to be kept secret and some critics argued the release would make the United States less safe.

Michael Hayden, who led the CIA under George Bush, said officers would now be more timid and allies more reluctant to share sensitive intelligence.

"If you want an intelligence service to work for you, they always work on the edge. That's just where they work," Mr Hayden said.

Now, he said, foreign partners would be less likely to co-operate with the CIA because the release showed they "can't keep anything secret".

Meanwhile human rights advocates said Mr Obama should not have assured the CIA that officers who conducted the interrogations would not be prosecuted if they used methods authorised by Bush lawyers in the memos.

But Mr Obama said in a statement: "Nothing will be gained by spending our time and energy laying blame for the past."