Welcomed with thunderous cheers, President Barack Obama told a European audience on Friday that he is setting a dramatic goal of "a world without nuclear weapons." The new American president opened a town-hall style gathering with the declaration, saying he would outline details in Prague in the coming days. "Even with the Cold War now over, the spread of nuclear weapons or the theft of nuclear material could lead to the extermination of any city on the planet," Obama said, previewing a planned speech. He was in the midst of his first European trip as president as he sought to strengthen the United States' standing in the world while working with foreign counterparts to right the troubled global economy. Obama said the United States shares blame for the crisis, but that "every nation bears responsibility for what lies ahead - especially now."