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SAN FRANCISCO (KTVU) - The mayor of Osaka, Japan sent a letter terminating San Francisco's longest-standing sister city relationship Tuesday, citing objections over a "Comfort Women Memorial" depicting women used for sex by Japanese soldiers during World War II.

The memorial statues were erected in a public park on California Street and given to the city in 2015 as a gift by the group Comfort Women Justice Committee.

In the ten-page letter written in English, Osaka Mayor Hirofumi Yoshimura sent San Francisco Mayor London Breed a detailed list of concerns which Yoshimura said he and his predecessor had raised seven different times since the city accepted the Comfort Women Memorial in 2015.

The sister city relationship with Osaka was San Francisco's first, dating back more than six decades to October 7, 1957. A sign post, along Market Street at Hallidie Plaza shows arrows pointing in the direction of Osaka and San Francisco's 18 other sister cities.

"We do not want to break off the relationship with Osaka," said Liilian Sing, Co-Chair of the Comfort Women Justice Coalition.

Lillian Sing and Julie Gang are co-chairs of the Comfort Women Justice Committee that paid for the memorial and a prominent billboard that recently went up alongside the highway leading up to the lower deck of the Bay Bridge. Sing and Gang say the goal is to remember the thousands of women who were euphemistically called "comfort women" to provide sex for Japanese military troops.

"It's a beautiful statue. It represents the three countries with the largest number of comfort women, China, Korea and the Philippines,' said Sing.

"The Diet as a whole, which is like the Congress, legislature of the United States. They have never passed a resolution that acknowledged the history or apologized." said Julie Tang.

Osaka's mayor says he does not deny the trauma inflicted on "comfort women."

"It goes without saying that the use of "comfort women" by Japanese soldiers before and during World War II was an unforgivable act that violated the dignity and human rights of women," he wrote.

Mayor Yoshimura says he objects to the memorial plaque and "the inscription that presents uncertain and one-sided claims as historical facts."

One point of contention is the inscription which says it honors the "hundreds of thousands" of comfort women from World War II. The number has been debated by historians arguing a wide range of estimates from tens of thousands to the widely held 200,000, depending on the parameters used.

Yoshimura also delves into the controversial topic of whether Japan's apologies have been sincere and sufficiently comprehensive. The Japanese government reached an agreement with South Korea in 2015 which involved issuing an apology and establishing an $8.8 million fund to help survivors. Some say that was insufficient.

Mayor Yoshimura stated in his letter, "This issue should not be treated as an issue specific solely to the Japanese military."

Mayor Lond Breed's office responded saying they received the letter. At this point, they have no intention of taking down any of the sister city signs or ending the grassroots relations.

Mayor Breed's communication director Jeff Cretan released a statement Tuesday saying "It's unfortunate that Mayor Yoshimura no longer wishes to maintain ties between the governments of San Francisco and Osaka. However, we will remain sister cities via the people-to-people ties maintained by our San Francisco-Osaka Sister City Committee and their counterparts in Osaka."

Members of the Sister City Committee said Tuesday night that they plan to continue cultural exchanges and education program such as the San Francisco Osaka Youth Network which provides summer exchange programs for students.