North Korean state media warned on Tuesday of a nuclear attack on the United States at any sign of American aggression, as a U.S. Navy strike group steamed toward the western Pacific - a force U.S. President Donald Trump described as an "armada".

Trump, who has urged China to do more to rein in its impoverished ally and neighbor, said in a Tweet that North Korea was "looking for trouble" and the United States would "solve the problem" with or without Beijing's help.