China says it has lodged an official complaint with Tokyo, after the mayor of a Japanese city again denied the well-documented pre-World War Two massacre of several hundred thousand Chinese civilians by Japanese troops in 1937.

Nanjing officials suspended all contacts late Tuesday with its Japanese sister city, Nagoya. The action came hours after the Chinese consulate in Nagoya protested Mayor Takashi Kawamura's assertion that the so-called Nanjing massacre “probably never happened.”

Chinese and Western historians estimate that between 200,000 and 300,000 Chinese were killed by Imperial Japanese forces during a six-week period beginning in December 1937.

Many Chinese, including war survivors, still voice resentment toward Japan.

Kawamura also raised the ire of China in 2009, when he told the Nagoya city council that the Nanjing death toll cited by Beijing was inflated.

In 2005, protests erupted across much of East Asia over Japan's approval of revisionist history textbooks that also minimize the impact of its wartime activities. Protesters also targeted Japanese efforts to gain a permanent seat on the United Nations Security Council.