Mark Halperin and John Heilemann's book "Double Down: Game Change 2012" notes President Obama commenting on drone strikes, reportedly telling his aides that he's "really good at killing people."
The quote from the book was first reported in Peter Hamby's review in the Washington Post.
The White House had not officially commented on the alleged remarks, but senior adviser Dan Pfeiffer dismissed a series of reports from the book, including one that showed Obama campaign officials deciding whether to replace Vice President Joe Biden with Hillary Clinton.
"The president is always frustrated about leaks," Pfeiffer said on ABC's "This Week." "I haven't talked to him about this book. I haven't read it. He hasn't read it. But he hates leaks."
The Bureau of Investigative Journalism estimates that a total of 2,528-3,648 people have been killed by CIA drone strikes in Pakistan since 2004, and between 416-948 of them being civilians. The group labels 326 of such events as "Obama strikes."
President Obama has taken considerable criticism for the expansion of the CIA targeted killing program - especially from the man who was awarded the Nobel Peace Prize in 2009 for "his extraordinary efforts to strengthen international diplomacy and cooperation between peoples."