The United States brutalised scores of terror suspects with interrogation tactics that turned secret CIA prisons into chambers of suffering and did nothing to make America safer after the September 11 2001 attacks, Senate investigators have concluded.

The Senate Intelligence Committee's torture report, years in the making, accused the CIA of misleading its political masters about what it was doing with its "black site" captives and deceiving Americans about the effectiveness of its techniques.

The report was the first public accounting of tactics employed after the September 11 terrorist attacks, and it described far harsher actions than had been widely known. Tactics included confinement to small boxes, weeks of sleep deprivation, simulated drowning, slapping and slamming, and threats to kill, harm or sexually abuse families of the captives.

President Barack Obama declared some of the past practices to be "brutal, and as I've said before, constituted torture in my mind. And that's not who we are," he told the Spanish-language TV network Telemundo in an interview.

"One of the things that sets us apart from other countries is that when we make mistakes, we admit them," he said.

Mr Obama added that releasing the information was an important "so that we can account for it, so that people understand precisely why I banned these practices as one of the first acts I took when I came into office, and hopefully make sure that we don't make those mistakes again".

Then president George W Bush approved the programme through a covert finding in 2002, but he was not briefed by the CIA about the details until 2006.

At that time Mr Bush expressed discomfort with the "image of a detainee, chained to the ceiling, clothed in a nappy and forced to go to the bathroom on himself".

The report produced revulsion among many, challenges to its veracity among some lawmakers and a sharp debate about whether it should have been released at all.

Republican senator John McCain, tortured in Vietnam as a prisoner of war, was out of step with some fellow Republicans in welcoming the report and endorsing its findings.

"We gave up much in the expectation that torture would make us safer," he said in a Senate speech. "Too much."

Five hundred pages were released, representing the executive summary and conclusions of a still-classified 6,700-page full investigation.

Senator Dianne Feinstein, the Democratic committee chairman whose staff prepared the summary, branded the findings a stain on US history.

"Under any common meaning of the term, CIA detainees were tortured," she declared, commanding the Senate floor for an extended accounting of the techniques identified in the investigation.

The report catalogued the use of ice baths, death threats, shackling in the cold and much more. Three detainees faced the simulated drowning technique known as waterboarding. Many developed psychological problems.

But the "enhanced interrogation techniques" did not produce the results that really mattered, the report asserts in its most controversial conclusion.

It cites CIA cables, emails and interview transcripts to rebut the central justification for torture - that it thwarted terror plots and saved American lives.

In a statement, CIA director John Brennan said the agency made mistakes and has learned from them.

But he also asserted the coercive techniques "did produce intelligence that helped thwart attack plans, capture terrorists and save lives".

The report, released after months of negotiations with the administration about what should be censored, was issued as US embassies and military sites worldwide fortified security in case of an anti-American backlash.

Earlier this year, Ms Feinstein accused the CIA of infiltrating Senate computer systems in a dispute over documents as relations between the investigators and the spy agency deteriorated, the issue still sensitive years after Mr Obama ordered a halt to any such interrogation practices upon taking office.

After al Qaida operative Abu Zubaydah was arrested in Pakistan in 2002, the CIA received permission to use waterboarding, sleep deprivation, close confinement and other techniques. Agency officials added unauthorised methods, the report says.

At least five men in CIA detention received "rectal rehydration", a form of feeding through the rectum. The report found no medical necessity for the treatment.

At least three in captivity were told their families would suffer, with CIA officers threatening to harm their children, sexually abuse the mother of one man, and cut the throat of another man's mother.

Zubaydah was held in a secret facility in Thailand, called "detention Site Green" in the report. Early on, with CIA officials believing he had information on an imminent plot, Zubaydah was left isolated for 47 days without questioning, the report says. Later, he was subjected to the panoply of techniques. He later suffered mental problems.

He was not alone. In September 2002, at a facility referred to as Cobalt - the CIA's "Salt Pit" in Afghanistan - detainees were kept isolated and in darkness. Their cells had only a bucket for human waste.

Redha al-Najar, a former Osama bin Laden bodyguard, was the first prisoner there. CIA interrogators found that after a month of sleep deprivation, he was a "broken man".

But the treatment got worse, with officials lowering food rations, shackling him in the cold and giving him a nappy instead of toilet access.

Gul Rahman, a suspected extremist, received enhanced interrogation there in late 2002, shackled to a wall in his cell and forced to rest on a bare concrete floor in only a sweatshirt. The next day he was dead. A CIA review and post-mortem examination found he died of hypothermia.

US Justice Department investigations into that and another death of a CIA detainee resulted in no charges.

Khalid Sheikh Mohammed, the September 11 mastermind, received the waterboarding treatment 183 times. At one point, he was waterboarded for not confirming a "nuclear suitcase" plot the CIA later deemed a scam. Another time, his waterboarding produced a fabricated confession about recruiting black Muslims in Montana.

After reviewing six million agency documents, investigators said they could find no example of unique, life-saving intelligence gleaned from coercive techniques. The report claims to debunk the CIA's assertion its practices led to bin Laden's killing.

In Geneva, the United Nations' special rapporteur on human rights and counter-terrorism, Ben Emmerson, said, the report confirmed "that there was a clear policy orchestrated at a high level within the Bush administration, which allowed to commit systematic crimes and gross violations of international human rights law".

He said international law prohibits the granting of immunity to public officials who have engaged in acts of torture, including both the actual perpetrators and senior government officials who authorised the policies.

"The individuals responsible for the criminal conspiracy revealed in today's report must be brought to justice, and face criminal penalties commensurate with the gravity of their crimes."

The report was issued as US embassies and military sites worldwide strengthened security in case of an anti-American backlash.

The US embassies in Afghanistan, Pakistan and Thailand warned of the potential for anti-American protests and violence after the release of the Senate report. The embassies also advised Americans in the three countries to take appropriate safety precautions, including avoiding demonstrations.

After Navy Seals killed Osama bin Laden in Pakistan in May 2011, top CIA officials secretly told lawmakers that information gleaned from brutal interrogations played a key role.

Then-CIA director Leon Panetta repeated that assertion in public and it found its way into a critically acclaimed movie about the operation, Zero Dark Thirty. It depicts a detainee offering up the identity of bin Laden's courier, Abu Ahmad al-Kuwaiti, after being tortured at a secret CIA interrogation site.

As it turned out, bin Laden was living in al-Kuwaiti's walled family compound, so tracking the courier was the key to finding the al Qaida leader.

But the CIA's story, like the Hollywood one, is not true, the Senate report on CIA interrogations concludes in a 14,000-word section of the public summary.

"A review of CIA records found that the initial intelligence obtained, as well as the information the CIA identified as the most critical or the most valuable on Abu Ahmad al-Kuwaiti, was not related to the use of the CIA's enhanced interrogation techniques," it says.

CIA officials disagree and maintain that detainees subjected to coercive tactics provided crucial details.

"It is impossible to know in hindsight whether we could have obtained ... the same information that helped us find bin Laden without using enhanced techniques," the agency said in its written response.

Former Polish president Aleksander Kwasniewski said that during his term Poland offered the CIA a site for a secret prison but did not authorise the harsh treatment of inmates.

It is the first time a Polish leader has admitted the country hosted a secret CIA site. Reports say it operated from December 2002 until the autumn of 2003.

Mr Kwasniewski was in power from 1995 to 2005. He said the activity in Poland was terminated under pressure from its leaders.

Until now, Polish leaders at the time have denied the site's existence but their successors ordered a probe in 2008.