United States President Donald Trump has started his trip to Beijing by telling Chinese President Xi Jinping "it's an honour to be your friend", even as his counterpart offered a cautionary warning about avoiding a possible clash between the two nations.The stark contrast in tone underscored just how far apart the leaders remain on thorny issues, including the war in Iran, trade disputes and the US relationship with Taiwan — and suggests that Trump and Xi's highly anticipated meetings are likely to be stronger on pageantry and symbolism than major breakthroughs.In remarks before their meeting at the Great Hall of the People moved behind closed doors, Trump was full of platitudes, saying of Xi: "You're a great leader Trump administration officials also want to work toward establishing a board of trade with China to address commercial differences between the countries.But neither side has yet offered concrete details on what might come out of the three-day visit at a time when Beijing's close economic ties to Iran could complicate matters.Trump's trip comes as Iran continues to dominate his domestic agenda and stoke fears about the prospect of a weakening US economy