Vice President Joe Biden has sworn in John Brennan as Director of the Central Intelligence Agency.

Brennan assumed his post at a ceremony in the Roosevelt Room of the White House Friday. Brennnan is a long-time CIA official who supports the administration's use of drones to kill terror suspects overseas.

The U.S. Senate confirmed President Barack Obama's nomination of Brennan Thursday.

Kentucky Republican Rand Paul threatened to hold up the vote indefinitely over the White House drone policy, filibustering against the Brennan confirmation by talking non-stop on the Senate floor for nearly 13 hours Wednesday. He demanded the Obama administration specify limits on using drone strikes to attack American terror suspects on U.S. soil.

Attorney General Eric Holder sent Paul a brief letter stating that the president does not have the authority to kill a U.S. citizen not engaged in combat on U.S. soil.

Holder said earlier this week that while the president has no intention of ordering a drone strike within the United States, he could do so under an "extraordinary circumstance."

The Obama administration has used drones to kill terror suspects abroad, including U.S. citizens.

Senators on the Intelligence Committee demanded to see the top secret legal opinions justifying such attacks before sending Brennan's nomination to the full Senate.