US President Donald Trump says 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.

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.​

Source: Reuters