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The cargo ship Kang Nam 1 has long been on a watch-list of North Korean vessels suspected of illicit trading. But it recently emerged from the shadows at the center of a cat-and-mouse game in Asian waters, tracked by U.S. warships, maritime reconnaissance planes and satellites under a United Nations resolution that bans Pyongyang from exporting arms of any kind and using the profits to sustain its military.

Since leaving the North Korean port of Nampo on June 17, the freighter has become a test case of how the U.N. Security Council resolution, passed unanimously after North Korea's nuclear explosive test on May 25, will be implemented. In turn, this may indicate how major powers will deal with Iran if it continues its suspected pursuit of nuclear...