FILE - In this Oct. 29, 2010 file photo, Deputy National Security Adviser for Homeland Security and Counterterrorism John Brennan briefs reporters at the White House in Washington. Brennan, now President Barack Obama's nominee to be CIA director, withdrew from consideration for the job in 2008 amid criticism over the agency's use of harsh interrogation techniques, like waterboarding, against terrorist suspects. This time, in 2013, he's making it clear he strongly opposes such practices. Former and current U.S. intelligence officials say Brennan wasn't so vocal a decade ago. (AP Photo/Charles Dharapak, File)

A Republican critic of the Obama administration's drone policy has succeeded in blocking a vote on John Brennan's nomination to be director of the CIA.

Sen. Rand Paul announced Wednesday he was mounting a filibuster against President Barack Obama's pick to lead the spy agency and he demanded that Obama or Attorney General Eric Holder issue a statement making clear that drones would not be used in the United States to kill terrorism suspects who are American citizens.

Senate Majority Leader Harry Reid said he planned to file a motion to bring debate over the Brennan nomination to an end. But he would need 60 votes in the 100-member Senate to do that.

Brennan's nomination won approval Tuesday by the Senate Intelligence Committee by a 12-3 vote.