The CIA has completed a report that challenges the findings of a Senate investigation of the agency’s interrogation program, according to U.S. officials who said the response cites errors in the congressional probe and disputes its central conclusion that harsh methods used against al-Qaeda detainees failed to produce significant results.

The classified CIA document is expected to be delivered to the Senate Intelligence Committee on Thursday by Director John Brennan during a closed-door meeting with the committee’s chairman, Sen. Dianne Feinstein (D-Calif.), and ranking Republican Saxby Chambliss (Ga.).

The agency’s rebuttal is the most detailed defense that the CIA has assembled to date of one of the more controversial programs in its history, one that employed simulated drowning and other brutal measures to get information from al-Qaeda captives before the agency was ordered to close its secret prisons in 2009.

But the agency’s response and the 6,000-page congressional report it addresses both remain classified, making it unclear whether portions of either document will be made public. A CIA spokesman declined to comment on the agency’s response, but current and former U.S. intelligence officials said it is sharply critical of the course of the committee’s investigation as well as its conclusions.

Despite lawmakers’ conclusions that harsh interrogations were ineffective, “anyone who was around and involved in the program knows that’s not right,” said a former high-ranking U.S. intelligence official. “I don’t know how they could fail to say that actually it was effective, and you can separate that from whether you approve of it or not.”

The CIA report catalogues errors that teams of agency analysts found in the committee’s research. It also questions the panel’s methodology, noting that the committee collected millions of internal CIA cables and other documents on the interrogation program, but it did not interview anyone directly involved.

A committee aide said the panel had requested interviews but was rebuffed.

A senior aide on the Senate Intelligence Committee declined to comment on the CIA response, except to say that it had not yet been delivered.

The competing documents reflect the extent to which views of the CIA interrogation program remain bitterly divided more than a decade after the agency first used waterboarding on an al-Qaeda operative, Abu Zubaida, who was captured in Pakistan and remains in U.S. custody at Guantanamo Bay, Cuba.

The issue has created a dilemma for Brennan just months into his tenure as director. During his confirmation hearing this year, Brennan said he was dismayed by the committee’s findings and questioned whether he had been misled about the program when he served as a senior agency executive in the years after the Sept. 11, 2001, attacks.

Brennan now faces the prospect of delivering a report that could anger lawmakers if it is perceived as defending a program that has been widely condemned, or alienating CIA colleagues if it is seen as capitulating to critics.

The committee’s investigation took several years to complete and was approved in December on a 9 to 6 vote that broke largely along party lines. It is said to include detailed chronologies of the interrogations of senior al-Qaeda detainees.

Feinstein said in a statement at the time that the report “uncovers startling details about the CIA detention and interrogation program and raises critical questions about intelligence operations and oversight.” The creation of “clandestine ‘black sites’ and the use of so-called enhanced-interrogation techniques were terrible mistakes.”