CIA Director John Brennan is defending his agency from accusations in a Senate report that it used inhumane interrogation techniques against terrorist suspects with no security benefits to the U.S.

Brennan opened a rare news conference Thursday by recounting the horrors of the Sept. 11, 2001 attacks, his agency's determination to prevent another such assault and the fact that CIA officers were the first to fight and early to die in the Afghanistan war.

He conceded unauthorized and in some cases abhorrent methods were used against captives. He said it was "unknowable" whether so-called enhanced interrogation techniques managed to get useful intelligence out of terrorism suspects.

"I have already stated that 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 said.

"But let me be clear. We have not concluded that it was the use of EITs (enhanced interrogation techniques) within that program that allowed us to obtain useful information from detainees subjected to them. The cause-and-effect relationship between the use of EITs and useful information subsequently provided by the detainee is, in my view, unknowable," he added. 

'We asked the agency to go take steps and put in place programs that were designed to catch the bastards who killed 3,000 of us on 9/11 and make sure it didn't happen again, and that's exactly what they did.' - former U.S. vice-president Dick Cheney

He asserted the CIA "did a lot of things right" in a time when there were "no easy answers."

The CIA and several of its past leaders, along with former vice-president Dick Cheney, have been stepping up a campaign to discredit the five-year U.S. Senate investigation into the CIA's harrowing interrogation practices after Sept. 11, concerned that the historical record may define them as torturers instead of patriots and expose them to legal action around the world.

The Senate intelligence committee's report doesn't urge prosecution for wrongdoing, and the Justice Department has no interest in reopening a criminal probe. But the threat to former interrogators and their superiors was underlined as a United Nations special investigator demanded those responsible for "systematic crimes" be brought to justice, and human rights groups pushed for the arrest of key CIA and Bush administration figures if they travel overseas.

Current and former CIA officials pushed back Wednesday, determined to paint the Senate report as a political stunt by Senate Democrats tarnishing a program that saved American lives. It is 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.

CIA inflicted suffering beyond legal authority: report

Hayden was singled out by Senate investigators for what they said was a string of misleading or outright false statements he gave in 2007 about the importance of the CIA's brutal treatment of detainees in thwarting terrorist attacks. He described the focus on him as "ironic on so many levels" as any wrongdoing predated his arrival at the CIA. "They were far too interested in yelling at me," Hayden said in an email to The Associated Press.

The intelligence committee's 500-page release concluded that the CIA inflicted suffering on al-Qaeda prisoners beyond its legal authority and that none of the agency's "enhanced interrogations" provided critical, life-saving intelligence. It cited the CIA's own records, documenting in detail how waterboarding and lesser-known techniques such as "rectal feeding" were actually employed.

The CIA is now in the uncomfortable position of defending itself publicly, given its basic mission to protect the country secretly. Its 136-page rebuttal suggests Senate Democrats searched through millions of documents to pull out only the evidence backing up predetermined conclusions. "That's like doing a crossword puzzle on Tuesday with Wednesday's answer's key," the CIA said in an emailed statement.

Challenging one of the report's most explosive arguments — that harsh interrogation techniques didn't lead to Osama bin Laden — the CIA pointed to questioning of Ammar al-Baluchi, who revealed how an al-Qaeda operative relayed messages to and from bin Laden after he departed Afghanistan. Before then, the CIA said, it only knew that courier Abu Ahmad al-Kuwaiti interacted with bin Laden in 2001, when the al-Qaeda leader was accessible to many of his followers. Al-Kuwaiti eventually led the U.S. to bin Laden's compound in Pakistan.

Poring over the same body of evidence as the investigators, the CIA insisted most of the 20 case studies cited in the Senate report actually illustrated how enhanced interrogations helped disrupt plots, capture terrorists and prevent another Sept. 11-type attack. The agency said it obtained legal authority for its actions from the Justice Department and White House, and made "good faith" efforts to keep congressional leaders informed.

Report 'full of crap,' VP Cheney says

Former CIA officials responsible for the program echoed these points in interviews.

John McLaughlin, then deputy CIA director, said waterboarding and other tactics transformed Sept. 11 mastermind Khalid Sheikh Mohammed into a U.S. "consultant" on al-Qaeda.

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

Cheney Paul Iraq

Former U.S. vice-president Dick Cheney, pictured here in April 2013, has been critical of a Senate report that condemns the CIA's use of torture. (Olivia Harris/Associated Press)

Former vice-president Dick Cheney also pushed back, saying in a Fox News interview that the Senate report "is full of crap."

In no uncertain terms, Cheney said the CIA's approach to interrogating terror suspects was necessary after the Sept. 11 attacks, and the people who carried them out were doing their duty.

"We asked the agency to go take steps and put in place programs that were designed to catch the bastards who killed 3,000 of us on 9/11 and make sure it didn't happen again, and that's exactly what they did, and they deserve a lot of credit," he said, "not the condemnation they are receiving from the Senate Democrats. "

And former top CIA officials published a website pointing out decade-old statements from senators Dianne Feinstein and Jay Rockefeller in apparent support of agency efforts. The two Democrats spearheaded the Senate investigation.

The intelligence committee's Republicans issued their own 167-page "minority" report and said the Democratic analysis was flawed, dishonest and, at $40 million, a waste of taxpayer money. Feinstein's office said Wednesday most of the cost was incurred by the CIA in trying to hide its record.

With files from Reuters