The Mexican authorities say six police officers and a 17-year old girl have been killed in a shootout in the country's most violent city Ciudad Juarez<br/><br/>A police spokesman said the incident occurred when police agents were ambushed by suspected drug gang members.<br/><br/>Correspondents say the violence in Juarez is due to a two-year turf battle between rival drug cartels for control of one of the most lucrative routes for illegal drugs into the US from Mexico.