WASHINGTON—President Donald Trump emphasized that the U.S. is willing to take unilateral action against North Korea if China doesn’t move to contain the burgeoning nuclear power, as he put trade and the military threat from Pyongyang at the top of the agenda of his planned meeting with Chinese President Xi Jinping this week.

In his comments, Mr. Trump looked to tie U.S. imports of Chinese goods with China’s cooperation on North Korea. The Trump administration, which has made narrowing the trade deficit a priority, has called...