Osaka: US President Donald Trump set the tone Thursday for what promises to be a stormy G20 summit by lashing out at friends and foes alike over trade tariffs and foreign policy.

The long-running US-China trade war looked set to dominate the two-day meeting of world leaders in Osaka from Friday but clashes also loomed over climate and hotspots including North Korea and Iran. On board Air Force One en route Japan, Trump fired off a characteristically bullish tweet, chiding long-standing ally India for "unacceptable" tariffs on American goods.