Zhu Chengshan, director of the Memorial Hall of the Victims of the Nanjing Massacre by Japanese Invaders, said that a substantial amount of evidence, including text and video material, could prove that the massacre was an undeniable fact.

"The truth cannot be distorted or denied by an individual's assumption," Zhu said.

The Nanjing Massacre took place on Dec 13, 1937, when Japanese troops occupied the then capital of China. More than 300,000 Chinese civilians and disarmed soldiers were killed and thousands of women raped.

Roots of the dispute

The dispute began on Monday when Nagoya's Mayor Takashi Kawamura told a visiting delegation from Nanjing that he doubted that the Nanjing Massacre of 1937 ever took place.

Kyodo News Agency reported that Kawamura, whose father was in Nanjing in 1945, said that he believed only "conventional acts of combat" took place there.

"Why were people in Nanjing kind to Japanese soldiers only eight years after the incident?" Kawamura asked, referring to his father's memories. "I could go to Nanjing and attend a debate on the history of the city, if necessary."

Reports said Liu Zhiwei, a member of the Standing Committee of the Communist Party of China Nanjing Municipal Committee who led the delegation, didn't challenge the mayor directly at the time. Instead, he said: "Nanjing people still love peace. We need to learn from history and not to continue enmity."

Nanjing established sister-city relations with Nagoya in Japan in 1978.