A senate report has found that the CIA covered up brutal interrogation methods of terror suspects, including sleep deprivation, 'rectal feeding' and chaining captives in a 'dungeon'.

The agency's methods were also "not effective" and failed to secure information that thwarted any terrorism threats, according to the much anticipated findings.

Senator Dianne Feinstein said that "CIA detainees were tortured" and the agency misled the public and Congress about the interrogations.

She said the techniques were "far more brutal than people were led to believe" and the CIA made "inaccurate" claims about the intelligence they yielded.

Much of the programme, which ran from 2002-06, was developed and operated by two external contractors, according to the report.

On Tuesday morning, the Senate Intelligence Committee published a 480-page executive summary of the 6,200-page report compiled by Democrats on the panel.

Examples of brutality outlined in the findings include:

• One detainee interrogated at a secret prison died from hypothermia after being held partially nude and chained to a concrete floor.
• Some detainees were deprived of sleep for up to 180 hours, at times with their hands shackled above their heads. Others underwent "rectal feeding" and "rectal hydration" without any clear medical need.
• One secret CIA prison at an unspecified location was described as a "dungeon", where detainees were kept shackled in pitch-black cells, while bombarded with loud noise and music.
• Al Qaeda detainee Abu Zubaydah was waterboarded 83 times and on one occasion became "completely unresponsive with bubbles rising through his open full mouth", though he survived. The CIA planned to cremate him if he died.
• In one facility, guards used what they called "rough takedowns" in which detainees were hooded and dragged down a hallway while being slapped and punched.

Senate Majority Leader Harry Reid told the Senate floor: "The implications of this report are profound.

"Not only is torture wrong, but it doesn't work ... It got us nothing except a bad name."

Senator Feinstein said the programme was "a stain on our values and on our history".

The report is the first public accounting of the CIA's use of what critics call torture on al Qaeda detainees held at "black" sites in Europe and Asia or at Guantanamo Bay.

The report, which took years to produce, charts the history of the CIA's "Rendition, Detention and Interrogation" programme, which then-president George W Bush authorised in the aftermath of the 2001 attacks.

The committee's bottom-line conclusion is that harsh interrogations did not produce a single critical intelligence nugget that could not have been obtained by non-coercive means.

CIA director John Brennan conceded the CIA detention and interrogation programme "had shortcomings and that the agency made mistakes".

Reacting to the report, President Barack Obama said in a written statement the Bush-era techniques "did significant damage to America's standing in the world and made it harder to pursue our interests with allies and partners".

Republican Senators Marco Rubio and Jim Risch issued a statement calling the release of the report "reckless and irresponsible".

But their colleague, John McCain, who was himself tortured while serving in Vietnam, said the CIA methods had damaged America's reputation.

The White House said on Monday that security had been beefed up at US facilities worldwide to brace for any worldwide backlash to the report.