The head of the US spy agency CIA has defended his agency from accusations in a Senate report that it tortured terrorism suspects with no security benefits to the country.

John Brennan said on Thursday that while his agency "fell short of holding accountable some officers" who went beyond the legal limits on interrogation, he asserted that the CIA "did a lot of things right" in a time when there were "no easy answers".

"Our reviews indicate that the detention and interrogation program produced useful intelligence that helped the United States thwart attack plans, capture terrorists and save lives," Brennan told a news conference at the agency's Virginia headquarters.

Summary: Key findings in CIA torture probe

On Tuesday, a US Senate report condemned the CIA for brutality and deception. The "enhanced interrogation techniques [EITs]" were authorised by the administration of George W Bush after the September 11, 2001 attack on the US.

Brennan also said that it was "unknowable" if those techniques - widely condemned by American and international critics as torture - led to the capture and death of Osama bin Laden.

"We have not concluded that it was the use of EITs within that programme that allowed us to obtain useful information from detainees subjected to them," Brennan said.

"It was our job to carry it out," he said, referring to the order of the Bush administration to interrogate suspects in the wake of attacks on the World Trade Centre twin towers.

He conceded that unauthorised and in some cases "abhorrent" methods were used against captives.

Accountability demanded

After Brennan's speech, the American Civil Liberties Union (ACLU) expressed concern that if officials are not held accountable for the conduct detailed in the report, the government will adopt these methods again in the future.

"The fact that President Obama’s CIA director believes that these methods remain a policy option for the next administration shows why we need a special prosecutor. We have to ensure that this never happens again,” ACLU Executive Director Anthony D Romero said.

The heavily redacted 480-page report covered the treatment of around 100 suspects rounded up by US operatives between 2001 and 2009 on terrorism charges.

Senate Intelligence Committee chair Dianne Feinstein said the techniques used by the CIA were "far more brutal than people were led to believe" and that "coercive techniques regularly resulted in fabricated information" from detainees.

100+ interview reports, oral and written testimony, CIA’s response and numerous CIA meetings all contributed to study. #ReadTheReport — Sen Dianne Feinstein (@SenFeinstein) December 11, 2014

As Brennan spelled out his objections to the report, the office of Feinstein unleashed a barrage of tweets challenging him. One said that "every fact" in the committee's report was based on CIA records, cables or other evidence.

Another Feinstein tweet reads, "No evidence that terror attacks were stopped, terrorists captured or lives saved through use of EITs."

Current and former CIA officials have defended the CIA's conduct.

The report was a "one-sided study marred by errors of fact and interpretation - essentially a poorly done and partisan attack on the agency that has done the most to protect America,'' former CIA directors George Tenet, Porter Goss and Michael Hayden wrote in a Wall Street Journal opinion piece.

The Senate report concluded that the CIA inflicted suffering on al-Qaeda prisoners beyond its legal authority. It cited the CIA's own records, documenting in detail how waterboarding and lesser-known techniques such as "rectal feeding" were

actually employed.

In a formal 136-page rebuttal, the CIA suggested Senate Democrats searched through millions of documents to pull out only the evidence backing up predetermined conclusions.

Tenet, the director on September 11, 2001, said the interrogation programme "saved thousands of Americans lives" while the country faced a "ticking time bomb every day".