U.S. President Donald Trump has said Japan should have shot down the North Korean missiles that flew over the country before landing in the Pacific Ocean earlier this year, diplomatic sources said Saturday.

The revelation comes just ahead of Trump's arrival in Japan on Sunday, at the start of a trip to five Asian nations. Threats from North Korea's nuclear and missile development will be high on the agenda when Trump holds talks with Japanese Prime Minister Shinzo Abe on Monday.

Trump questioned Japan's decision not to shoot down the missiles when he met or spoke by phone with leaders from Southeast Asian countries over recent months to discuss how to respond to the threats from North Korea, the sources said.

The U.S. president said he could not understand why a country of samurai warriors did not shoot down the missiles, according to the sources.

In defiance of international sanctions imposed to compel Pyongyang to abandon its nuclear weapon and missile development programs, North Korea test-launched ballistic missiles on Aug. 29 and Sept. 15 that flew over Japan's northernmost main island of Hokkaido before falling into the Pacific Ocean.

But Japan's Self-Defense Forces did not try to intercept the missiles, with the government saying the SDF had monitored the rockets from launch and judged they would not land on Japanese territory.

Defense Ministry officials said there were also legal issues to clear, and it would have been very difficult to shoot down the missiles given the altitudes at which they flew.

On Sept. 3, North Korea also conducted its sixth and most powerful nuclear test by detonating what it said was a hydrogen bomb that could be mounted on an intercontinental ballistic missile.

While the United States and its allies and partners have been pressing North Korea to denuclearize, the Trump administration says it is keeping all options -- including military action -- on the table in dealing with the situation.