A leak of the major findings of a landmark Senate inquiry into the CIA’s post-9/11 torture of terrorism detainees led, on Friday, to intensified pressure on the White House and the CIA to release the inquiry speedily and with a minimum of redactions.

The classified study, prepared by the Senate select committee on intelligence, concluded that the CIA’s interrogations, secret detentions and outsourced torture sessions were “brutal, and far worse than the agency communicated to policymakers.”

More suspected terrorists underwent the agency’s post-9/11 treatment, which largely lasted from 2002 to 2006, than the CIA has publicly admitted, according to the report’s findings, which were first reported by McClatchy. Last week, committee chairwoman Dianne Feinstein of California stated that the Senate investigated the cases of 100 detainees – dozens more than previously known to have gone through the CIA’s so-called “interrogation, detention and rendition” programs.

In addition to misleading policymakers, the Senate report charges the CIA with selectively and leaking classified and inaccurate information to journalists in order to portray the program in a positive light.

“The CIA manipulated the media by co-ordinating the leak of classified information, which inaccurately portrayed the effectiveness of the agency’s enhanced interrogation techniques,” the committee found.

The agency also, according to the report, provided factually inaccurate information to Bush administration lawyers, who relied on it to concoct the legal theories that underpinned an apparatus of torturous interrogations and detentions that quickly spread to US military facilities at Guantánamo Bay, Iraq and Afghanistan.

The study took four years and $40m to complete, and has brought the relationship between the CIA and the Senate panel overseeing it to perhaps its lowest ebb in history.

Not only does Langley contend that the committee has developed a factually inaccurate picture of the since-shuttered program, it has appealed to the Justice Department to open a criminal inquiry into Senate staffers for taking a classified agency document out of a secured facility – a move Feinstein has called an attempt at intimidation.

In March, on the Senate floor, Feinstein accused the CIA of breaching a network barrier on a system it set up to allow the agency to share documents with the committee electronically. She said the move meant the agency spied on the Senate staff, which she said violated the separation of powers outlined in the constitution.

Despite the acrimony, the White House announced last week that the CIA will lead the executive-branch panel that will recommend how much of the Senate report’s executive summary, findings and recommendations to make public, a decision blasted by human-rights groups and intelligence scholars as a conflict of interest.

On Thursday, 40 Democratic members of the House of Representatives wrote to President Obama urging him to declassify the committee’s executive summary and major findings “expeditiously and in their entirety.”

“The American people need and deserve a full account of the actions that were taken in their name through the use of torture and enhanced interrogations on detainees. As you have said publicly, the report must be declassified “so that the American people can understand what happened in the past’,” the legislators wrote.

After the committee voted last week to authorize declassification of aspects of its report, Feinstein challenged the administration to release the executive summary, findings and recommendations with minimal redactions and within 30 days. She said that the committee could hold a subsequent vote on declassifying the entire 6,000-plus page study, which some observers understood as a tactic to give the committee leverage in case the CIA’s redactions of the current portions up for review are extensive.

“Some ... do not want this report to become public and are seeking to discredit it,” Feinstein wrote on Thursday in the Washington Post, along with former committee chairman Jay Rockefeller, a West Virginia Democrat.

According to the leaked conclusions, the committee found that that the agency poorly managed its interrogation and detention efforts. It relied extensively on outside contractors for design and implementation, especially “two contract psychologists,” whom an earlier Senate Armed Services Committee investigation identified as Bruce Jessen and Jim Mitchell. Both men were influential in retrofitting techniques that had been designed to train captured US troops to survive and resist torture by foreign adversaries for use on detainees.

“Numerous internal critiques and objections concerning the CIA’s management and use of the Detention and Interrogation [sic] were ignored,” according to the committee findings. Those internal critiques include a now partially declassified 2004 inspector general’s report.

Human rights groups cited the leaked conclusions to pressure the administration to fully declassify the Senate report’s major aspects – and to take responsibility for its release out of the CIA’s hands.

"The legal foundation for this program was always broken, but this also shows that it was resting on thin air. These conclusions only reinforce that torture is a brutal, unlawful practice that is unnecessary for protecting our national security,” said former navy general counsel Alberto Mora in a statement released by Human Rights First.

“It’s important to have as much of the report made public as possible to put these findings in context. The White House should lead the declassification process and ensure that the American people can understand the true costs of our experiment with torture.”

In a letter he sent to President Obama on Friday, Senator Mark Udall, a Democrat from Colorado, wrote, "[T]he most pressing reason for the White House to step in and manage this process is the CIA's clear conflict of interest on this issue and its demonstrated inability to face the truth about this program. … The CIA is certainly entitled to issue a public response to the Committee's study, but not to impede the declassification of the study itself."