U.S. President Donald Trump said on Friday that North Korea was a "big problem", but assured Japanese Prime Minister Shinzo Abe that issues surrounding the secretive Asian state would be resolved.

"It is very much on our minds... It's a big problem, it's a world problem and it will be solved. At some point it will be solved. You can bet on that," Trump said sitting alongside Abe in a bilateral meeting ahead of a Group of Seven summit.

North Korea's growing nuclear and missile threat is seen as a major security challenge for Trump, who has vowed to prevent the country from being able to hit the United States with a nuclear missile, a capability experts say Pyongyang could have some time after 2020.