Former CIA lawyer John Rizzo on "enhanced interrogation": "I don't think I had any other choice"
Details of the CIA's "enhanced interrogation" techniques, considered by many to be torture, are set to be revealed in a long-awaited report.
The Senate Intelligence Committee's report is expected to find that such interrogations failed to yield life-saving information.
The techniques were used on al-Qaeda terrorism suspects in the years following the 9/11 attacks on the US.
Security was increased at US facilities around the world ahead of publication.
Embassies and other sites were taking precautions amid "some indications" of "greater risk", a White House spokesman said.
The Senate committee's report runs to more than 6,000 pages, drawing on huge quantities of evidence, but it remains classified and only a 480-page summary will be released.
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Analysis: Jon Sopel, BBC North America editor
What more can we learn about the CIA's interrogation programme from this heavily redacted report? Based on leaks, Tuesday's release seems to answer three major questions
Were the interrogation methods - torture if you like - more extensive and more brutal than previously admitted? It looks like the conclusion is "Yes"
Did these interrogation techniques deliver life-saving intelligence to the US? That answer appears to be "No"
Were CIA officials at the time honest with the White House on what the programme was getting up to? Again, "No"
We can also expect the beginning of a counterblast of speeches, editorials and comments from those in charge of the CIA at the time attacking the Congressional report.
But White House officials - while supportive of the release in principle - nervously dispatched Secretary of State John Kerry to encourage the committee to think twice about releasing this report into a volatile world. That didn't work.
Delayed publication
As well as detailing the controversial methods used by CIA operatives in an effort to extract information from high-value suspects, the report is expected to say harsh interrogations failed to deliver appropriate results.
Publication of the report has been delayed amid disagreements in Washington over what should be made public.
Senate Intelligence Committee chair, Dianne Feinstein, who initiated the investigation five years ago, was involved in months of discussion with the White House about what could be released.
She is expected to brief journalists as the findings are published on the committee's website.
President Barack Obama halted the CIA interrogation programme when he took office in 2009, and has acknowledged that the methods used to question al-Qaeda prisoners amounted to torture.
During the presidency of George W Bush, the CIA operation against al-Qaeda - known internally as the Rendition, Detention and Interrogation - saw as many as 100 suspected terrorists held in "black sites" outside the US.
They were interrogated using methods such as waterboarding, slapping, humiliation, exposure to cold, and sleep deprivation.
Leaks about the Senate report first emerged in August this year, prompting Mr Obama to declare: "We tortured some folks. We did some things that were contrary to our values."
The US president added that he believed officials at the time had used harsh methods because of the "enormous pressure" to prevent another attack on the US in the wake of 9/11.
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