Prime Minister Shinzo Abe has kept a diplomatically low profile, particularly over historical issues, focusing instead on economic and other domestic matters ahead of the July Upper House election.

But if his Liberal Democratic Party fares well in the polls and adds an Upper House majority to the one it already commands in the Lower House, he may again attempt to push a nationalistic agenda.

A key focus will be his stance on the "comfort women," the women and girls forced into sexual slavery in Japanese-occupied Asia during the war.