North Korean leader Kim Jong-un's latest letter to U.S. President Donald Trump was apparently sent through a direct channel between the adversaries rather than using South Korea as a mailman.

This suggests that U.S.-North Korea talks have been going on behind the scenes despite the collapse of their summit in Hanoi in February.

Pundits are reduced to guesswork but surmise that the letter was passed to the U.S. in the border truce village of Panmunjom, which it polices, and Ambassador to Seoul Harry Harris may have hand-carried it to Trump when he flew to Washington for a business gathering early this week.

Trump told reporters at the White House on Tuesday he received the "beautiful" letter "yesterday" without mentioning how it was delivered.

