US President Donald Trump said on Saturday he would "absolutely" be willing to talk on the phone to North Korean leader Kim Jong Un and that he hopes a positive development results from talks between North Korea and South Korea.

North Korea agreed on Friday to hold official talks with South Korea next week, the first in more than two years, hours after Washington and Seoul delayed a military exercise amid a standoff over Pyongyang’s nuclear and missile programs.

Trump, answering questions from reporters at the presidential retreat at Camp David, Maryland, expressed a willingness to talk to Kim but not without preconditions.

"Absolutely, I would do that," Trump said. "I have no problem with that at all."

Trump and Kim have exchanged insults ever since Trump took office, with Trump repeatedly calling Kim "rocket man" for testing nuclear weapons and ballistic missiles.

Earlier this week Trump dismissed Kim's taunt that the North Korean leader has a nuclear button on his desk, saying he has a bigger button.

The talks between North Korea and South Korea are expected to cover the Winter Olympics, to be held in South Korea next month, and inter-Korean relations.

Trump suggested the talks might lead to an easing of tensions and took credit for the diplomatic breakthrough, saying it was a result of his steady pressure.

"Look, right now they're talking Olympics. It's a start, it's big start. If I weren't involved they wouldn't be talking at all right now," he said.

Kim "knows I'm not messing around. I'm not messing around. Not even a little bit, not even one percent. He understands that," said Trump.

"If something can come out of those talks, that would be a great thing for all of humanity, that would be a great thing for the world," he said.