The inspector general's report defused a rare public feud between the CIA and one of its oversight committees in Congress. The dispute stemmed from an investigation by the intelligence committee of the "enhanced interrogation" techniques used by the CIA in the years after the Sept. 11, 2001, terrorist attacks, such as waterboarding, sleep deprivation and confinement in small spaces.
"These are positive first steps," Sen. Dianne Feinstein, the committee chairman, said in a statement responding to Brennan's apology. "This IG report corrects the record and it is my understanding that a declassified report will be made available to the public shortly."
In March, Feinstein, a California Democrat who usually champions the intelligence agencies, took to the Senate floor to protest that the CIA may have broken the law and violated the Constitution's provisions on separation of powers by secretly monitoring computers being used by committee staff and withholding some documents in violation of an agreement.
The CIA, in turn, said that some Senate staff members had surreptitiously removed classified files from a CIA facility and asked the Justice Department to investigate.
The Justice Department said last month that there was insufficient evidence to continue criminal investigations into the CIA's or the Senate committee staff's actions.
Brennan's apology is an effort by the Obama administration to ease tensions between the CIA and the Senate committee as the lawmakers prepare to release a report sharply critical of the intelligence agency's 2001-2006 detention and interrogation program, said two U.S. officials.
The report found that the use of waterboarding and other harsh interrogation techniques produced little timely, accurate and valuable intelligence in the war on terrorism, according to the officials, who have read it and agreed to speak only on the condition of anonymity because it hasn't been declassified. Former officials of intelligence agencies and President George W. Bush's administration dispute that conclusion.
The Senate committee also found that CIA officials either withheld information from or misled then-Secretary of State Colin Powell and other administration officials and the congressional oversight committees, the two officials said.
Sen. Mark Udall, a Colorado Democrat on the intelligence committee, said in a statement that Brennan has failed to deliver on promises to change the CIA's culture and respect "vigorous and independent congressional oversight."
"From the unprecedented hacking of congressional staff computers and continued leaks undermining the Senate Intelligence Committee's investigation of the CIA's detention and interrogation program to his abject failure to acknowledge any wrongdoing by the agency, I have lost confidence in John Brennan," Udall said.
The White House spokesman defended Brennan's leadership of the CIA Thursday.
"Director Brennan has taken all of the kinds of responsible steps to address the situation," Josh Earnest said. "He is somebody who had a very difficult job, who does that job extraordinarily well."