U.S. President Donald Trump said on May 26 that North Korea, which has conducted a series of recent missile tests, was a "big problem" on the U.S. foreign policy agenda.
Trump spoke after a meeting with Japanese Prime Minister Shinzo Abe ahead of the start of a Group of Seven (G7) summit on the Italian island of Sicily.
"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.
Meanwhile, the White House said Trump and Abe agreed to expand sanctions against North Korea for its continued development of ballistic missile and nuclear programs.
"They also agreed to further strengthen the alliance between the United States and Japan, to further each country's capability to deter and defend against threats from North Korea," a statement said.
North Korea's nuclear and missile programs are seen as a major security challenge for the Trump administration.
The U.S. president has vowed to prevent the country from being able to hit the United States with a nuclear missile, a capability experts say Pyongyang could acquire sometime after 2020.
Trump's administration has been seeking to convince China and Russia to put more pressure on North Korea.
But at a joint press conference after a meeting in Moscow, Chinese Foreign Minister Wang Yi and Russian Foreign Minister Sergei Lavrov had words of warning for South Korea and the United States.
Wang said that that Beijing and Moscow are calling on North Korea to respect UN resolutions on its nuclear program, but that China also expects South Korea to make efforts to resume talks with Pyongyang.
Lavrov said Russia and China agree that the development of North Korea's nuclear program should not be used as an excuse for deploying elements of a U.S. global antimissile system on the Korean Peninsula.
With reporting by Reuters, dpa, and AP