Marc Knapper, deputy assistant secretary of state responsible for Japan and Korea, told a Washington think tank it was critical to ensure “productive and constructive relationships” between the allies in the face of shared challenges posed by North Korea, Russia and China.

He said Japan and Korea each suffer consequences when their bilateral ties worsen and we believe that each bears the responsibility for improvement in their relations.

The unusually frank comments underlined the depth of concern in Washington about the dispute between the two long-term allies which has brought the relationship between Seoul and Tokyo to arguably its lowest ebb in more than half a century.