Premier Giorgia Meloni said Thursday that the European Union must take concrete action to boost its competitiveness if it is to "think big" and face up to today's international challenges after she hosted a pre-summit with German Chancellor Friedrich Merz and Belgian Prime Minister Bart De Wever before an informal meeting of EU leaders.     "The challenge is to see whether the European Union can provide concrete, effective, immediate responses to competitiveness issues, because there's no more