WASHINGTON (AFP) - The United States (US) Senate confirmed counterterrorism expert John Brennan to be the next Central Intelligence Agency (CIA) director on Thursday, filling a third crucial position on President Barack Obama's national security team.

The Senate voted 63-34 with several Republicans flocking to approve Brennan following a dramatic 13-hour filibuster the night before by Senator Rand Paul over the possible use of drones to conduct targeted killings on US soil.

Mr Obama hailed the Senate's move, praising Mr Brennan's "determination to keep America safe, his commitment to working with Congress, his ability to build relationships with foreign partners and his fidelity to the values that define us as a nation".

The confirmation of Mr Brennan, who has 25 years of prior experience at the CIA, comes after senators also gave their nod to Mr John Kerry to lead the State Department and to Mr Chuck Hagel as Pentagon chief.

Despite his reservations, Mr Paul was among several Republicans who backed Brennan, the architect of a controversial "targeted killing" policy that has seen targets such as Al-Qaeda operatives killed in Pakistan and Yemen.

The Kentucky senator had delayed up the nomination, seeking clarification from the White House over whether it was US policy to allow the killing by a drone strike of a "non-combatant American citizen on US soil". He got his answer on Thursday, when US Attorney General Eric Holder wrote to tell Mr Paul that this was not the policy.

After he received the letter, Mr Paul said that it showed his battle was worthwhile.

The unmanned aerial drone program had emerged as the most contentious element of Mr Brennan's nomination to head the Central Intelligence Agency.

On Tuesday, Mr Holder had said that, while Obama had "no intention" of ordering drone strikes on US soil, the scenario could be possible if there was an "extraordinary circumstance" such as an attack similar to 9/11.

Mr Paul, who began his filibuster of Mr Brennan's CIA nomination shortly before noon on Wednesday, finally yielded the floor after midnight, to a round of applause.

Mr Paul acknowledged that US drone strikes have proven effective in places like Pakistan and Yemen, including a strike on US-born radical preacher Anwar al-Awlaki, whom Mr Paul branded a traitor.

But he added: "if you're going to kill non-combatants, people eating dinner, in America, there have to be some rules."

The New America Foundation estimates that US drones have conducted about 350 attacks since 2004, most of them under Obama, who ramped up the program after taking over the White House from his predecessor George W. Bush.

Between 1,963 and 3,293 people were killed by the strikes, including 261 to 305 civilians, according to the think-tank.

Mr Obama stressed that "timely, accurate intelligence is absolutely critical to disrupting terrorist attacks, dismantling Al-Qaeda and its affiliates, and meeting the broad array of security challenges that we face as a nation".

"John's leadership, and our dedicated intelligence professionals, will be essential in these efforts," he added.