Singapore Prime Minister Lee Hsien Loong has urged Japan to admit to its misdeeds from World War II so it can play a more active role in the region.

"Japan needs to acknowledge past wrongs, and Japanese public opinion needs to be more forthright in rejecting the more outrageous interpretations of history by right-wing academics and politicians," Lee said in a keynote speech at Friday's opening of the Asia Security Summit conference, also known as the Shangri-La Dialogue.

"Japan has already expressed remorse or apologies for the war in general terms," he said. "But on specific issues like the 'comfort women' and the Nanjing Massacre, its positions have been less unequivocal."