At the top of the list is Haiti's Port-au-Prince with 139 homicides per 100,000 residents, followed by five cities in Mexico: Colima, Manzanillo, Acapulco, Tijuana and Ciudad Obregón.

As the sounds of automatic gunfire in a central working-class Port-au-Prince neighborhood once more sent desperate residents fleeing for refuge on Thursday, hundreds of miles away in ...