"I got a very beautiful letter from Kim Jong Un yesterday," Trump said. "It was a very positive letter."

"He wasn't happy with the war games," Trump added, referring to new military exercises between US forces and the South Korean military that began this week.

"As you know, I've never liked it either. I've never been a fan. And you know why? I don't like paying for it," the US leader said.

Trump received Kim's three-page letter on Thursday after Pyongyang undertook four missile tests in the past two weeks that it said were a response to the joint exercises between the South and the United States.

While the weapons fired were not the medium- and long-range ballistic missiles that have posed an implicit threat to Japan and the United States, they were seen to be a new type of extremely fast, short-range guided ballistic missile that could pose a potent danger to South Korea.

On Tuesday North Korea threatened more weapons tests, and said the US-South Korea war games were "an undisguised denial and a flagrant violation" of the diplomatic process between Pyongyang, Washington and Seoul.

Trump continued to play down the missile tests and said he could have a third summit with Kim in the future.

"I think we'll have another meeting," he said.

"In the meantime I'll say it again. There have been no nuclear tests. The missile tests have all been short-range. No ballistic missile tests, no long-range missiles," he said.