South Korea and China on Friday condemned new Japanese textbooks that say that islands at the centre of separate territorial disputes belong to Japan, the latest in a series of disputes between Tokyo and neighbours Seoul and Beijing.
The elementary school textbooks describe islands called Dokdo in Korean and Takeshima in Japanese as Japan's "sovereign territory" and say South Korean occupation is unlawful.
The books also say China's claims to islands known as Senkaku in Japan and Diaoyus in China in the East China Sea are unfounded.
South Korean First Vice Minister Cho Tae-yong called in Japan's ambassador to Seoul to protest and the ministry warned of worsening ties.
"If (Japanese) Prime Minister Shinzo Abe who declared just three weeks ago he stands by the 'Kono Statement' now tries to conduct education for elementary school children that distorts and hides its history of colonial invasion, he is not only breaking his own promise but also committing the mistake of isolating its next generation from international society," the ministry said.
The statement refers to an apology made by former cabinet secretary Yohei Kono in 1993 which recognised the Japanese government involvement in taking women, mostly Korean, to work in military brothels as sex slaves during the war.
Both China and Korea suffered under Japanese rule, with parts of China occupied in the 1930s and Korea colonized from 1910 to 1945.
Chinese Foreign Ministry spokesman Hong Lei said Japan had to take a "sincere attitude" towards facing up to history.
"Japan should teach its next generation in these textbooks that the Diaoyus are China's, and that Japan has illegally snatched them away," he told a daily news briefing.
Hong added that China was also highly concerned about a Japanese Foreign Ministry policy paper, which also claimed the islands as Japan's and said China was trying to change the status quo with force.
"It neglects the facts, wantonly blackens China's name and unreasonably criticises China. We are extremely concerned and very dissatisfied," he said.
Japan's ties with South Korea and China have long been poisoned by what Beijing and Seoul consider Tokyo's failure to atone for its wartime past.
Anger has mounted over the past year after Abe's visit to a controversial Tokyo shrine honouring war criminals among Japan's war dead.
Tokyo had worked hard to ease tension with Seoul last month under pressure from Washington to improve ties and drew a concession from South Korean President Park Geun-hye who agreed to sit down for a meeting with Abe and U.S. President Barack Obama on the sidelines of a security summit in the Hague.
(Reporting By Sohee Kim; Additional reporting by Ben Blanchard in BEIJING; Editing by Nick Macfie)