The head of United Airlines apologized to customers on Monday after videos on social media showed an Asian passenger screaming while being removed from his seat and then - bleeding from the face after hitting his head - being limply dragged down the aisle of a full flight at Chicago O'Hare International Airport after refusing to give up his seat.

"This is an upsetting event to all of us here at United. I apologize for having to re-accommodate these customers," United CEO Oscar Munoz said in a statement. "Our team is moving with a sense of urgency to work with the authorities and conduct our own detailed review of what happened."

Chicago's Aviation Department said one of its officers involved in dragging the man off the flight did not follow standard operating procedures and has been placed on leave.