Up to 450 migrants fleeing Libya are thought to have drowned this week, with the bulk of the rescue effort falling on the Italian navyPope Francis has appealed for a greater international effort to help Italy cope with the growing humanitarian crisis in the Mediterranean, after a week in which about 450 migrants are believed to have drowned.Speaking after meeting the new Italian president, Sergio Mattarella, at the Vatican on Saturday, the pontiff said: “It is evident that the proportions of the phenomenon demand much greater involvement.