An ambulance transports injured victims beside a burning bus at the site of an explosion in Karachi on December 29, 2012. At least four people were killed and dozen wounded when a loud explosion ripped apart a passenger bus outside the railway station in the Pakistani port city of Karachi, the nature of the explosion could not be ascertained. AFP PHOTO/Asif HASSAN        (Photo credit should read ASIF HASSAN/AFP/Getty Images)