The presidents of China and the Republic of Korea shared their nations' concerns over Japan's new military policy on Friday, days after Tokyo announced a landmark shift in its military stance.
They also shared their countries' common painful past under Japanese militarism.
Observers said the two leaders' position, with President Xi Jinping's suggestion of joint memorial activities to mark their nations' victory over Japan, signals a subtle change in East Asian geopolitics.
Xi, making a two-day visit to Seoul, met his South Korean counterpart Park Geun-hye at a special luncheon meeting, their second meeting in two days.
His visit follows Japanese Prime Minister Shinzo Abe's announcement on Tuesday that Japan's military has the right to collective self-defence and troop deployment overseas, marking a radical change in the country's postwar pacifist stance.
Ju Chul-ki, senior foreign affairs and security adviser to Park, said the two presidents called attention to the fact that many countries and more than half of the Japanese people oppose the reinterpretation.
Xi and Park also voiced regrets over Japan's recent review of the 1993 apology for wartime sex slavery, saying the review was aimed at "damaging and disparaging" the apology.
The Kono Statement, an official apology made by then Japanese chief cabinet secretary Yohei Kono in 1993, acknowledged that Japan was involved in forcing more than 200,000 women, mostly Koreans, to serve in military brothels.
On June 20, the Japanese Cabinet announced the results of its reexamination of the statement. It said the ROK government intervened in the wording of the apology, indicating this was the result of closed-door political dealings.
Xi and Park also agreed that international coordination to resolve the Democratic People's Republic of Korea nuclear issue can be breached if sanctions imposed on Pyongyang for its nuclear programme are mishandled.