A new exhibition started Monday at a museum dedicated to the 1937 massacre in Nanjing of Chinese citizens by the Japanese military, ahead of this weekend's anniversary of the incident.

The exhibition, featuring documents and items on the theme of "victory" against Japanese wartime aggression, is in a newly built facility adjacent to the Memorial Hall of the Victims in Nanjing Massacre in the eastern Chinese city.

It is the latest in a series of events to commemorate the 70th anniversary this year of Japan's defeat in World War II.

China will hold a national-level ceremony Sunday at the memorial hall to mark the 78th anniversary of the massacre.

China has designated Dec. 13 as a national memorial day for the incident's victims. Last year, President Xi Jinping delivered a speech at the first state ceremony in Nanjing, the provincial capital of Jiangsu.

On Dec. 13, 1937, Japanese forces took control of the city, the Chinese capital at the time, back when it was known as Nanking. Both in the run-up to the city's capture and during the weeks that followed, Japanese troops killed a large number of Chinese civilians.

However, Japanese and Chinese historians are divided on the number of victims.

The often-tense relationship between Japan and China has been improving despite remaining differences.

But China's successful bid earlier this year to include documents on the rampage in the Memory of the World program by UNESCO has irked the Japanese government.

Japanese officials have criticized the U.N. cultural agency — an entity that should be neutral in sensitive political and historical issues — for "unilaterally" registering the Chinese dossier without allowing Japan to access them for verification.

China is expected to soon publicly unveil a statue recently set up at the memorial hall to mark the inclusion of the records to the UNESCO program.