NANJING - ?The first volume of an encyclopedia detailing the Nanjing Massacre was released on Sunday in Nanjing, capital of east China's Jiangsu Province.

The encyclopedia, composed of four volumes of over 8,000 entries, exposes the crimes of Japanese troops in Nanjing in over 40 days from late 1937 to early 1938.

Historians from some 10 countries, including China, Japan, the United States, Russia and Germany have contributed to the compendium.

Zhu Chengshan, curator of the Nanjing Massacre Memorial Hall, believes that as the first national memorial day on Dec. 13 draws near, publication of the book will promote historical truth and refute some right-wing Japanese slander.

Qi Houjie, one of the compilers and a former researcher with the Second Historical Archives of China, describes the work as mainly about the invaders' slaughter and sexual violence.

The Japanese right-wing's attempts to deny history has forced researchers to pay more attention to international cooperation and exchange, he said.

Japanese troops occupied Nanjing on Dec. 13, 1937, and began a six-week massacre. More than 300,000 Chinese people -- both soldiers who had laid down their arms and civilians - were killed and more than 20,000 cases of rape occurred.

The first volume deals mainly with the eve of the massacre. The other three volumes will be published by the end of next year, according to Zhu Tongfang, chairman of the Nanjing Publishing Group.