China's Xi Jinping has warned US President Donald Trump that their two countries could clash over Taiwan if the issue is not handled properly, an unusually harsh admonition that stood in contrast to the American leader's praise for his counterpart.The exchange at a highly anticipated summit in Beijing on Thursday underscored just how far apart Trump and Xi still are on thorny issues, including the war in Iran, trade disputes and Washington's relations with Taiwan, which is self-ruled but which