US government backing for the CIA's harsh interrogation methods set the tone for abuses by US troops towards detainees in Iraq, a US report says.

It was not appropriate simply to blame low-ranking officers for what occurred at Abu Ghraib prison, the report by the Senate Armed Services Committee said.

Top officials had sent the message that such acts were appropriate, it stated.

The report follows the release of Bush-era memos that justify the use of what some critics say amounts to torture.

The memos detail a range of methods the CIA could use on terrorism suspects under the previous government.

These included week-long sleep deprivation, forced nudity and the use of painful positions, as well as water-boarding - a technique which simulates drowning.