Osaka has ended a six-decade 'sister-city' relationship with San Francisco in protest over a statue honouring women forced to have sex with Japanese soldiers during World War II.
The mayor of Osaka, Hirofumi Yoshimura, wrote a letter to San Francisco to announce he was withdrawing his city from the relationship because of the statue.
It was erected on city property last year by California's Korean, Chinese and Filipino communities.
Historians say tens of thousands of women around Asia were sent to work in Japanese military brothels, often through coercion and deception.
Japan apologised in 1993 but the issue has remained an open rift with its neighbours, particularly South Korea, which has strong memories of Japan's colonisation from 1910 to 1945.
After a gradual pullback from the apology, Japan's government now denies that the women, called "comfort women" in Japanese, were forced into sexual slavery, citing a lack of official documentary proof.
They argue the statue in San Francisco and similar statues built in various countries wrongfully blame Japan.
Jeff Cretan, a spokesman for San Francisco mayor London Breed, said Mr Yoshimura's decision was "unfortunate" and but said the two cities would remain connected through "people-to-people ties."
The Japanese consulate in San Francisco declined to comment.
Lillian Sing, co-chair of the Comfort Women Justice Coalition, said Japan was afraid of the truth.
"Breaking the relationship over a memorial is outrageous and absurd," she said.
"It shows how afraid the Osaka mayor and Japanese prime minister are of truth and are trying to deny history."
Agencies contributed to this report
