By Chris Hogg
BBC News, Tokyo
A group of MPs from Japan's governing party is claiming the Chinese have exaggerated the number of people killed by Japanese troops in Nanjing in 1937.
China claims as many as 300,000 died in the assault
China claims that during the assault on the city around 300,000 people were killed by the Japanese.
In Tokyo the MPs, from the right wing of the governing Liberal Democratic Party, claimed a month-long study they organised showed 20,000 died.
At the end of the year China will mark the 70th anniversary of the attack.
They call it the 'rape of Nanking', the name of the city in English at the time of the incident.
Several films will tell the story of what happened there. Nanjing was the capital city of China.
After it fell to the Japanese Imperial Army on 13 December 1937, the occupiers terrorised the city's population. Many thousands were killed.
But some in Japan want to use the anniversary to promote their view that the death toll, cited by the Chinese, is a fiction.
China says 300,000 lost their lives in Nanjing. Some experts argue a more accurate estimate is between 150,000 and 200,000.
Shinzo Abe may face problems from the claim
These lawmakers say a month-long study of historical documents suggests there is no evidence that soldiers killed any more than 20,000. What is more, they say, the Japanese did not violate international law.
Clearly these are hugely provocative statements, but do they matter? The Japanese and Chinese governments are carrying out their own joint study.
The exercise is designed to try to reduce the chances that disputes over historical fact will derail efforts to improve relations between them.
But the announcement by these lawmakers will make life difficult for Japan's Prime Minister Shinzo Abe, a well-known conservative.
He will no doubt now be asked repeatedly whether he shares the views of this large contingent of his own party.
But watch for the response of the Chinese.
A measured response will signal that they are not prepared to allow history to dominate discussions between Beijing and Tokyo in the run up to this important anniversary. An angry one could signal trouble ahead.