The head of the CIA is to mount a damage-limitation exercise in response to a damning senate intelligence committee report on torture.

As the agency faces its gravest crisis in decades, John Brennan is expected to address growing pressure on the White House and the CIA to hold individuals to account for covering up the torture of terrorist suspects. Mark Udall, a Democratic senator, has called for a purge of top CIA officials, and a row has developed over whether the agency kept both Congress and the previous administration sufficiently informed of the programme.

Brennan, one of President Barack Obama’s most trusted security advisers, has sought to tread a fine line since the report was released on Tuesday. He said then that intelligence gained from enhanced interrogation techniques helped to “thwart attack plans, capture terrorists, and save lives”. However, the CIA no longer argues that torture works, with Brennan and the agency instead saying the efficacy of torture is “unknowable”.

Brennan will speak at the agency’s headquarters in Langley, Virginia, on Thursday.

The Senate’s report does not urge prosecution for wrongdoing, but the threat to former interrogators and their superiors was underlined when a UN special investigator demanded that those responsible for “systematic crimes” be brought to justice. Human rights groups have pushed for the arrest of key CIA and Bush administration figures if they travel overseas.

Current and former CIA officials have poured scorn on the report, describing it as a last gasp from Democrats who are about to lose the Senate. It 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”, the former CIA directors George Tenet, Porter Goss and Michael Hayden wrote in the Wall Street Journal.

The intelligence committee’s 500-page report concluded that the CIA inflicted suffering on al-Qaida 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.

Former vice-president Dick Cheney was among the most vociferous critics of the Senate report. Photograph Charles Dharapak/AP Photograph: Charles Dharapak/AP

Dick Cheney, the former vice-president, was among the most vociferous critics of the Senate report. In a Fox News interview, he dismissed the report as being “full of crap”. Cheney said the CIA’s approach to interrogating terror suspects was necessary after the 9/11 attacks, and the people who carried them out were doing their duty.

“We asked the agency to go take steps and put in place programmes 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.”

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

The intelligence committee’s Republicans issued their own 167-page “minority” report, which said the Democratic analysis was flawed, dishonest and, at $40m, a waste of taxpayer money.

Feinstein’s office said most of the cost was incurred by the CIA in trying to hide its record.

Udall, an outgoing member of the intelligence committee and a leading congressional critic of intelligence overreach, called for a clean sweep of the CIA leadership implicated in the report, and argued that the agency was continuing to mislead, with White House support.

“Director [John] Brennan and the CIA are continuing to wilfully provide inaccurate information and misrepresent the efficacy of torture. In other words, the CIA is lying,” Udall said in what may be his final major Washington address after he was defeated in November’s midterm elections.

But the White House strongly defended Brennan on Wednesday, denying that he had lied about any aspect of the torture inquiry.

“He is somebody who, I think, adheres to the highest ethical standard that you would expect of a government official, and I don’t think there’s any reason for anybody to question that,” said Josh Earnest, the White House spokesman.

Obama has acknowledged that torture had proved counter-productive by damaging the country’s moral authority, although he stopped short of agreeing with the Senate report that no useful intelligence was gathered that could not have been obtained elsewhere.