South Korea and China on Monday protested against Tokyo's review of a landmark 1993 apology to women, many of them Korean and Chinese, forced to work as wartime sex slaves in Japanese brothels, urging it to stop trying to whitewash history.
South Korean First Vice Foreign Minister Cho Tae-yong summoned Japanese Ambassador Bessho Koro to complain, saying Tokyo was trying to undermine its own apology when the history behind the issue of "comfort women" was recognised internationally.
"Japan must understand that the more the Abe government tries to undermine the Kono statement, the more its credibility and international reputation will suffer," Cho said.
"Comfort women" is the euphemism for women forced to serve in military brothels serving Japanese soldiers before and during World War Two.
South Korea has protested against the conclusion of a Japanese panel reviewing the 1993 statement named after then-Chief Cabinet Secretary Yohei Kono that the two countries had worked together on the sensitive wording of the apology.
It rejected the finding that South Korea was involved in the formulation of the apology, saying the document was a formal statement by the Japanese government and the facts behind the comfort women issue had never been up for discussion.
The topic of comfort women has long been a thorn in the two countries' ties. South Korea says Japan has not sufficiently atoned for the women's suffering and any attempt at questioning the legitimacy of the apology is an indication of its insincerity.
China's Foreign Ministry spokeswoman Hua Chunying also urged Japan to take steps to handle the problems of its historical legacy.
"Japan's so-called investigation once again reveals that it is unwilling to face up to history and is even attempting to whitewash or deny the true intentions of its crimes of invasion," Hua told reporters at a regular press briefing.
Japan invaded China in 1937 and ruled parts of it with a brutal hand for the next eight years.
The legacy of Japan's 1910-1945 colonial rule of the Korean peninsula has complicated ties between two strong allies of the United States in the region that are also, along with China, involved in diplomatic efforts to end North Korea's nuclear and missile programmes.
Japanese Prime Minister Shinzo Abe has questioned the Kono statement in the past and in what many saw as a nod to his conservative base, the government asked five experts to review it.
But mindful of the potential diplomatic fallout, Abe has also said he would not revise it.
A summary of the review by Japan's foreign ministry said that there had been "in-depth coordination on the language of the Kono statement between Japan and the Republic of Korea", the official name of South Korea.
The two sides are also locked in a dispute over a group of islands called Dokdo in Korean and Takeshima in Japanese and controlled by South Korea but claimed by Japan as well. China and Japan are also involved in a row over a chain of uninhabited islands in the East China Sea.