The US Senate has confirmed counterterrorism expert John Brennan to be the next Central Intelligence Agency director, filling another crucial position on President Barack Obama's national security team.

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

Obama welcomed the vote, praising 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 Brennan, who has 25 years of prior experience at the CIA, comes after senators gave their nod to John Kerry to lead the State Department and to Chuck Hagel as Pentagon chief.

Despite his reservations, Paul was among several Republicans who allowed the vote to go ahead for Brennan, the architect of a controversial "targeted killing" policy that has seen al-Qaeda operatives killed in Pakistan and Yemen.

But Paul ultimately voted against Brennan's nomination.

Clarification sought

Paul, Kentucky senator, had delayed 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 Paul that this was not the policy.

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

The unmanned aerial drone programme had emerged as the most contentious element of Brennan's nomination to head the CIA.

On Tuesday, 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.

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

Proven effectiveness

Paul acknowledged that US drone strikes have proven effective in places like Pakistan and Yemen, including a deadly strike on US-born Muslim religious leader Anwar al-Awlaki, whom 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 escalated the programme 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.

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 said.