Meanwhile, U.S. President Donald Trump said that he received a "beautiful" letter from the North Korean leader this week.
Addressing reporters at the White House on Friday local time, Trump said that North Korean leader Kim Jong-un sent the letter, in which he expressed discontent with the Combined Command Post Training.
Trump described the 3-page letter as very beautiful, and spoke of possibilities for another meeting with Kim.
The U.S. President said he was never a fan of the training either, stressing that he doesn't like paying for it.
Trump also expressed concern over the souring ties between Seoul and Tokyo, saying that the two sides should get along because it puts Washington in a very bad position.