Tokyo has regarded the U.S.-led diplomatic push with Pyongyang with suspicion, and has sought to keep its interests on the table in the discussions by coordinating closely with its ally Washington.

"Japan fully supports President Trump's decision to make no easy compromise and at the same time continue productive discussions, and urge North Korea to take concrete action," Abe told reporters after a phone call with the U.S. president.

Trump and Abe spoke as the U.S. president headed back to Washington after a summit with North Korea's Kim Jong-un that ended abruptly, with plans for a joint statement scrapped.

Trump told reporters after two days of talks with the North Korean leader: "Sometimes you have to walk and this was just one of those times."

A key issue for Japan is the fate of several of its citizens kidnapped by North Korean agents, which Abe said Trump had once again raised during his discussions with Kim in the Vietnamese capital Hanoi.

"Japan and the U.S. will firmly maintain close cooperation towards resolving the abduction issue as well as the nuclear and the missile issues," he said.

Abe repeated his desire to hold his own face-to-face meeting with Kim, a prospect he has mooted several times without either Tokyo or Pyongyang publicly taking any concrete steps towards a summit.

"I'm determined to meet Chairman Kim Jong-un next time," he said..