BEIJING (Kyodo) -- Japan has asked China to bolster security to ensure the safety of its nationals in the country on the upcoming 87th anniversary of the 1937 massacre in Nanjing, Japanese government sources said Wednesday.

The request to Beijing, made by Japanese diplomatic establishments in China in the run-up to ceremonies to mark the anniversary on Friday, follows stabbing incidents in Suzhou and Shenzhen earlier this year, the sources said.

In June, a Japanese mother and her child were injured in Suzhou. A Japanese schoolboy was also killed in Shenzhen in September. Under such circumstances, Japanese schools in China have decided to close or hold classes online on Friday.

The scale of the killings by Japanese troops of civilians and soldiers during and in the weeks after the capture of Nanjing -- then the capital of Chiang Kai-shek's Nationalist Chinese government -- has been widely debated.

China claims the Japanese army slaughtered over 300,000 people in the Jiangsu Province city, formerly called Nanking. In contrast, estimates by Japanese historians place the death toll of Chinese civilians and soldiers between the tens of thousands and 200,000.