CIA chief nominee John Brennan will face a grilling soon at a Senate confirmation hearing.
The session comes as lawmakers were to receive secret papers setting out the rationale for drone strikes on Americans working with al-Qaeda abroad.
Members of President Barack Obama’s own Democratic party are concerned about John Brennan’s role in US drone policy.
He was a top CIA official under President George W. Bush.
John Brennan, 57, is also likely to face questions about his position on harsh interrogation techniques, such as waterboarding, that were used by the CIA while he was a senior official there.
Correspondents say that despite these concerns there has been no suggestion that members of the Senate Select Committee on Intelligence object to John Brennan’s nomination.
He is expected to be confirmed by the panel and later by the full Senate.
A vote to confirm former Republican Nebraska Senator Chuck Hagel as secretary of defence has been delayed amid opposition from some member of his own party.
John Brennan could face tough questions from Senator Ron Wyden, a Democratic member of the panel, who has vowed to press the nominee on drones.
Senator Wyden told MSNBC: “To make very clear, I am going to push for more declassification of these key kinds of [drone] programmes, and I think we can do that consistent with national security.”
On the eve of Thursday’s hearing, the committee released John Brennan’s answers to some preliminary questions.
John Brennan said he “had significant concerns and personal objections” about extreme interrogation techniques used by the CIA, adding he was “aware of the program but did not play a role in its creation, execution, or oversight”.
On drones, John Brennan said no new legislation was necessary for the US to conduct operations against al-Qaeda anywhere in the world.
He said individuals were targeted for killing “on a case-by-case basis through a coordinated interagency process” involving intelligence, military, diplomatic and other agencies.
John Brennan also acknowledged “instances when, regrettably and despite our best efforts, civilians have been killed”.
“It is exceedingly rare, and much rarer than many allege,” he added.
John Brennan’s hearing comes a day after the Department of Justice sent Congress documents laying out the legal rationale for targeting and killing US citizens who are suspected of working with terror groups.
Senator Dianne Feinstein, who chairs the Senate committee, said: “It is critical for the committee’s oversight function to fully understand the legal basis for all intelligence and counterterrorism operations.”
The justice department acted after NBC News published a leaked internal memo explaining some of the legal arguments.
John Brennan is believed to have been deeply involved.
The CIA has carried out drone strikes in Yemen, where three American citizens linked to al-Qaeda have been killed: Anwar al-Awlaki, his 16-year-old-son and Samir Khan.
Recent opinion polls have suggested that the US public generally supports the drone programme, especially when compared with the possibility of ground assault.
Republican Senator Lindsey Graham, who has opposed the appointment of Chuck Hagel as defence secretary, said: “The drone programme to me is a logical use of how you deal with an enemy combatant.”
John Brennan was considered for the top post at the intelligence agency in 2008.
But he withdrew his name from consideration amid protests over public statements he made on the CIA’s use of “enhanced interrogation techniques” such as waterboarding, which are viewed by many as torture.