Japan told China in late December that it wasn't appropriate for Chinese President Xi Jinping to say that 300,000 people were killed in the 1937 Nanking Massacre, government sources said on Wednesday.

Xi made the comment in a Dec. 13 speech at a ceremony marking the first national observance and the 77th anniversary of the massacre in the eastern Chinese city, which is now called Nanjing.

He called on Japan to own up to responsibility for the tragedy, saying that acknowledgment of the countries' shared troubled past is crucial to improving relations between them.

The Japanese government told China via a diplomatic channel after the speech that the figure is "different from Japan's position" and that it is "difficult to determine the concrete number of victims," according to the sources.

Among Japanese historians, death toll estimates from the Nanking Massacre generally range from tens of thousands up to 200,000.

The Japanese government admits that noncombatants were killed and there was looting during infamous episode.