The US Senate has confirmed John Brennan as the new director of the CIA.

BBC reports that Brennan has been confirmed Thursday by a 63-34 vote, after Senator Rand Paul marathon speech, known as a filibuster, delayed the vote.

Paul took to the Senate floor on Wednesday to question whether President Barack Obama had authority to order drone strikes on Americans on US soil.

Attorney General Eric Holder replied the president claimed no such power.

Paul - a critic of the use of drones - had demanded a pledge from either Obama or Holder that drones would not be used in the US to kill US citizens.

During his 13-hour speech, Paul read aloud from news articles critical of the drone program.

Also on Wednesday, Holder testified in front of a separate committee and was pressed on the drone program.

Senator Paul said Holder's responses in that hearing had come close to assuring him the government would not attack Americans with drones in the US, but he said he was "alarmed" by the difficulty of getting the White House to define clearly what qualified as a legitimate target.

On Thursday, Holder sent the following statement to Paul: "It has come to my attention that you have now asked an additional question: 'Does the president have the authority to use a weaponised drone to kill an American not engaged in combat on American soil?'

"The answer to that question is no."

Paul claimed victory and the Senate proceeded to a vote.

"With the bipartisan confirmation of John Brennan as director of the Central Intelligence Agency, the Senate has recognized in John the qualities I value so much. With John's 25 years of experience at the Agency, our extraordinary men and women of the CIA will be led by one of their own," President Barack Obama said in a statement.

Brennan's nomination was the latest in a series of tough confirmation battles as Obama rounds out his second term-leadership team.

Brennan was Obama's top counter-terrorism adviser and in this capacity helped oversee the drone program. He is largely credited with the planning of the 2011 raid that killed Osama bin Laden.

He is replacing General David Petraeus, who resigned last year after admitting to an extramarital affair.

Brennan was Obama's first choice for CIA Director and was to be nominated as early as 2008, but withdrew his name amid questions about his connection to interrogation techniques used during the administration of George W Bush. He denies having anything to do with the alleged torture of detainees at Guantanamo and even voiced strong opposition to them on several occasions.

Brennan visited Bulgaria shortly after the July 2012 terror act when 5 Israeli tourists and their Bulgarian bus driver were killed in an apparent suicide bombing at the Sarafovo airport in the Black Sea City of Burgas. He met in December with Bulgaria's Interior Minister, Tsvetan Tsvetanov, during the latter's trip to Washington DC.