US President Joe Biden, while in Seoul before heading to Japan on his first trip to Asia as US president, addressed North Korean leader Kim Jong-un with a simple message: "Hello. Period", Reuters reported.

Biden said he is "not concerned" by North Korea's new nuclear tests, which would be the first in nearly five years.

"We are prepared for anything North Korea does," he said.

But his scathing response to a question about what message he wants to convey to Kim underscored the administration's low-key approach to unresolved tensions with North Korea. This is a stark contrast to former President Donald Trump's ostentatious threats, summit meetings and love letters to Kim.

However, none of the president's approaches led to a major breakthrough, and North Korea has resumed testing its largest intercontinental ballistic missiles, with intelligence saying it is preparing for a new nuclear test, Reuters notes.