Japan and China should "freeze" their differences over the Senkaku Islands and focus on economic matters to improve strained relations, former Japanese Ambassador to China Uichiro Niwa said.

"Neither of us can compromise on those uninhabited islands even by 1 millimeter," Niwa said in a speech in Tokyo on Friday, referring to the East China Sea islet chain administered by Japan but also claimed by China, which calls it Diaoyu.

"Do we have to resolve the issue in five years? No." Niwa said. "Maybe 100 years later. So let us freeze the issue and do whatever we can on the economic front."