Guantanamo Bay
Taliban prisoners in orange jumpsuits sitting in holding area under the watchful eyes of military police at Camp X-Ray at Naval Base Guantanamo Bay, Cuba, during in-processing to the temporary detention facility on Jan. 11, 2002. Getty Images

The CIA used brutal torture methods against inhabitants at Guantanamo Bay and lied about their effectiveness, a four-year $40m (£25m) investigation has found.

The report concluded torture of suspects "regularly resulted in fabricated information", Senate intelligence committee chairwoman Dianne Feinstein said in a summary of the report's findings.

"During the brutal interrogations the CIA was often unaware the information was fabricated."

Detainees tortured at the hands of the CIA were subjected to a series of "enhanced interrogation techniques" which were far more brutal than previous feared.

Among the methods used by the CIA on terror suspects include extreme sleep deprivation, carrying out mock executions, "rectal dehydration" and waterboarding.

One suspect even died of hypothermia after he was chained naked to the floor inside the detention centre known as the Colbat or Salt Pit.

The report states how beginning with their first detainee Abu Zubaydah, the CIA applied its enhanced interrogation techniques with "significant repetition for days or weeks at a time".

It adds techniques such as slaps and 'wallings' (slamming detainees against a wall) were used in "combination [and] frequently concurrent with sleep deprivation and nudity".

In reaction to the report, US President Barack Obama said the methods were not aligned with American values.

In a statement, he said: "These techniques did significant damage to America's standing in the world and made it harder to pursue our interests with allies and partners."