Image copyright Getty Images Image caption The findings relate to CIA practices under former President George W Bush (File photo)

The CIA repeatedly misled the US government over the severity and effectiveness of its interrogation methods, the Washington Post reports.

A long-awaited US Senate report said that the CIA used secret "black sites" to interrogate prisoners using techniques not previously acknowledged.

These included dunking suspects in icy water and smashing a prisoner's head against a wall.

The findings stem from the time of former President George W Bush.

Officials familiar with the secret document said that the CIA's interrogation programme yielded little useful intelligence.

They also said that this intelligence had then been exaggerated so that the interrogation programme looked more effective than it actually was.

Internal divisions

Analysis The committee's accusations against the CIA were already very serious, but if this report is correct it blows a hole in the only argument in defence of "harsh interrogation" - that ugly as it was, it saved lives. The Post says the panel's report found such measures did not help in the hunt for Bin Laden or anything else of value, and that the CIA lied to pretend that vital evidence was obtained from prisoners after what most would consider torture, when in fact it was given freely much earlier. Republican sources have told the BBC there is an element of spin to put the CIA in the worst light. They will vote later in the week to make the 3,000-page report public. When it does it will put President Obama on the spot - he would rather not take on intelligence agencies acting under orders from a past White House. But some will argue such serious sins cannot go unpunished.

The report is the result of a wide-ranging investigation by the Senate intelligence committee into CIA activities which began in 2009.

The committee will meet on Thursday to decide on whether to send a summarised version to President Barack Obama for eventual public release.

Officials at the CIA's headquarters ordered officers to continue with harsh interrogations even after they were convinced that the prisoners had no more information to give, the Washington Post said.

One official said that almost all the valuable intelligence from al-Qaeda suspect Abu Zubaida was gained before he was waterboarded 83 times.

The report also spoke of divisions within the CIA in protest at the conditions prisoners were forced to endure.

A CIA spokesman told the Post the agency had not yet seen a final version of the report and so could not officially comment on its contents.

However, current and former officials told the paper privately that the 6,300 page study contained factual errors and misguided conclusions.

Earlier in March the head of the Senate intelligence committee accused the CIA of improperly accessing Senate computers during the investigation.

Senator Dianne Feinstein said that the alleged hacking "may have undermined the constitutional framework" of government oversight.