In his written submissions to the intelligence committee, Brennan declared that he had "significant concerns and personal objections to many elements of the EIT (enhanced interrogation technique)" program while it was under way.

"I voiced those objections privately with colleagues at the agency," Brennan continued, adding: "When I left the agency, I spoke publicly about those concerns."

He maintained that after being named White House counter-terrorism advisor, "I was put in a position to influence decisions related to EITS, such as how we handle interrogations, and I strongly support the president's ban on such techniques."

The CIA, which under Bush ran a network of secret prisons overseas where many of the so-called enhanced interrogations were conducted, was now "out of the detention business and it should stay that way".

Drone procedures

Questions about drones are expected after the leak this week of an unclassified Justice Department paper outlining Obama administration legal justifications for using armed drones to attack US citizens alleged to be involved in terrorist plots.

In his written submissions to the panel, Brennan said drone strikes were targeted "against specific al-Qaida terrorists in order to prevent terrorist attacks on the United States and to save American lives." He insisted those attacks were conducted "in full compliance with the law."

He said drone strikes hit their targets with "astonishing precision" and therefore "dramatically reduce the danger to US personnel and innocent civilians".

Leak investigations

Brennan is also likely to face questions about the news leaks, which are under federal investigation, although a congressional source said no evidence has emerged yet that Brennan played a role in some of the leaks.  

The US attorney in Baltimore is examining leaks about the alleged role of US agencies in cyber-warfare activities against Iran, including deployment of a virus known as Stuxnet.

The US attorney in Washington is looking into leaks  which led to the premature end of an undercover operation to infiltrate al-Qaida in the Arabian Peninsula (AQAP), the militant network's Yemen-based affiliate.

The Associated Press first reported last May that the US had disrupted a plot to bomb an airliner with a newly designed "underwear bomb".

Brennan subsequently advised former US counter-terrorism officials who are TV news pundits that the plot was never a serious threat because the US had "inside control".

This led to a statement by one TV pundit that the United States apparently had "somebody on the inside" of the plot. Reuters later learned that British intelligence agencies helped to plant an informant in AQAP, and that their operation, in which Saudi and US agencies also cooperated, had to be wound up prematurely because of leaks.