"It's a big problem", said Trump on Friday. It's a world problem.
Trump's remarks came ahead of a meeting with Japanese Prime Minister Shinzo Abe.
Tensions between Pyongyang and Washington over North Korea's continued missile programme have escalated since Trump took office in January.
The world leaders agreed with Abe's remarks, and shared a view that the North Korean threat should be regarded as the highest priority among the problems the world is facing. "You can bet on that", Trumps said in comments carried by Reuters. "We will be discussing many things including of course North Korea which is very much on our minds", he said in the Sicilian town of Taormina as he held bilateral talks with Abe at the start of the two-day G7 summit.
North Korea carried out two atomic tests previous year, and has accelerated its missile launch programme, despite tough United Nations sanctions aimed at denying Kim the hard currency needed to fund his weapons ambitions.
U.S. Secretary of State Rex Tillerson recently told a United Nations gathering that the U.S. would not hesitate to sanction other countries that support the North's illegal activities.
Abe said he meant to use the G7 summit to underscore the danger posed by the unpredictable regime in North Korea. But the Abe administration is opposed to that move in the current environment, not least because it could constitute recognition of North Korea as a nuclear weapons state.
Both the United States and Japan will also work together to increase their capacity to deter and defend threats coming from Pyongyang, the White House added.
"During the summit I emphasized that cooperation with Russian Federation and China is needed to solve the North Korea crisis".
China is said to be urging North Korea to exercise restraint, but has been reluctant to adopt strong sanctions that could lead to the collapse of the Kim Jong Un regime. The leaders met in Sicily, where they released a joint declaration stating that Pyongyang must immediately and fully comply with all relevant UN Security Council Resolutions and abandon all nuclear and ballistic missile programs in a complete, verifiable and irreversible manner.